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How to find the nth term in the following sequence: 1,1,2,2,4,4,8,8,16,16



The Next CEO of Stack OverflowHow to interpret the OEIS function for the “even fractal sequence” A103391 (1, 2, 2, 3, 2, 4, 3, 5, …)What will be nth term of the following sequence?How to find the nth term of this sequence?Number of possible ordered sequencesFind nth term of sequenceHow can i find the decimal values with a list of integers?Given a sequence find nth termFind nth term for below sequenceProve $lim_ntoinftyU_n = 1$ given $0 lt U_n - 1over U_nlt 1over n$ and $U_n>0$How to find the nth term in quadratic sequence?










2












$begingroup$


I'm having difficulty in finding the formula for the sequence above, when I put this in wolframalpha it gave me a rather complex formula which I'm not convinced even works properly but I'm sure there's a simple way to achieve this. I've searched for many similar sequences but couldn't find anything that helped me.



I'm thinking I'll most likely need to have a condition for even numbers and another for non even numbers.



Any help would be highly appreciated.










share|cite|improve this question







New contributor




Anonymous is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.







$endgroup$







  • 1




    $begingroup$
    How about using the floor function?
    $endgroup$
    – John. P
    19 mins ago
















2












$begingroup$


I'm having difficulty in finding the formula for the sequence above, when I put this in wolframalpha it gave me a rather complex formula which I'm not convinced even works properly but I'm sure there's a simple way to achieve this. I've searched for many similar sequences but couldn't find anything that helped me.



I'm thinking I'll most likely need to have a condition for even numbers and another for non even numbers.



Any help would be highly appreciated.










share|cite|improve this question







New contributor




Anonymous is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.







$endgroup$







  • 1




    $begingroup$
    How about using the floor function?
    $endgroup$
    – John. P
    19 mins ago














2












2








2





$begingroup$


I'm having difficulty in finding the formula for the sequence above, when I put this in wolframalpha it gave me a rather complex formula which I'm not convinced even works properly but I'm sure there's a simple way to achieve this. I've searched for many similar sequences but couldn't find anything that helped me.



I'm thinking I'll most likely need to have a condition for even numbers and another for non even numbers.



Any help would be highly appreciated.










share|cite|improve this question







New contributor




Anonymous is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.







$endgroup$




I'm having difficulty in finding the formula for the sequence above, when I put this in wolframalpha it gave me a rather complex formula which I'm not convinced even works properly but I'm sure there's a simple way to achieve this. I've searched for many similar sequences but couldn't find anything that helped me.



I'm thinking I'll most likely need to have a condition for even numbers and another for non even numbers.



Any help would be highly appreciated.







sequences-and-series






share|cite|improve this question







New contributor




Anonymous is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.











share|cite|improve this question







New contributor




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share|cite|improve this question




share|cite|improve this question






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asked 23 mins ago









AnonymousAnonymous

131




131




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New contributor





Anonymous is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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  • 1




    $begingroup$
    How about using the floor function?
    $endgroup$
    – John. P
    19 mins ago













  • 1




    $begingroup$
    How about using the floor function?
    $endgroup$
    – John. P
    19 mins ago








1




1




$begingroup$
How about using the floor function?
$endgroup$
– John. P
19 mins ago





$begingroup$
How about using the floor function?
$endgroup$
– John. P
19 mins ago











3 Answers
3






active

oldest

votes


















4












$begingroup$

These are just powers of two. So: $2^lfloor n / 2rfloor$






share|cite|improve this answer









$endgroup$












  • $begingroup$
    I'm not sure this works for everything, for example the 6th term should be 4 but 2^(3) = 8
    $endgroup$
    – Anonymous
    6 mins ago










  • $begingroup$
    This is assuming zero-indexing. So the first element is $n=0$. If you want it to be one-indexed then just subtract 1 from n in the formula.
    $endgroup$
    – Flowers
    3 mins ago


















1












$begingroup$

Alternatively, this is an example of a sequence where the $n$th term is a fixed linear combination of the immediately previous terms: We can write it as
$$a_n = 2 a_n - 2, qquad a_0 = a_1 = 1.$$
Using the ansatz $a_n = C r^n$ and substituting in the recursion formula gives $C r^n = 2 C r^n - 2$. Rearranging and clearing gives the characteristic equation $r^2 - 2 = 0$, whose solutions are $pm sqrt2$. So, the general solution is
$$a_n = A (sqrt2)^n + B(-sqrt2)^n = (sqrt2)^n [A + B(-1)^n] .$$
Substituting the initial values $a_0 = a_1 = 1$ gives a linear system in the coefficients $A, B$.






share|cite









$endgroup$




















    0












    $begingroup$

    The sequence is the powers of two, each repeated twice. We can encode the latter feature using the quantity $lfloor fracn2 rfloor$, which has values $0, 0, 1, 1, 2, 2, ldots$.




    So, the sequence is given (for appropriate indexing) by $$color#df0000boxeda_n := 2^lfloor n / 2 rfloor .$$







    share|cite|improve this answer









    $endgroup$













      Your Answer





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      3 Answers
      3






      active

      oldest

      votes








      3 Answers
      3






      active

      oldest

      votes









      active

      oldest

      votes






      active

      oldest

      votes









      4












      $begingroup$

      These are just powers of two. So: $2^lfloor n / 2rfloor$






      share|cite|improve this answer









      $endgroup$












      • $begingroup$
        I'm not sure this works for everything, for example the 6th term should be 4 but 2^(3) = 8
        $endgroup$
        – Anonymous
        6 mins ago










      • $begingroup$
        This is assuming zero-indexing. So the first element is $n=0$. If you want it to be one-indexed then just subtract 1 from n in the formula.
        $endgroup$
        – Flowers
        3 mins ago















      4












      $begingroup$

      These are just powers of two. So: $2^lfloor n / 2rfloor$






      share|cite|improve this answer









      $endgroup$












      • $begingroup$
        I'm not sure this works for everything, for example the 6th term should be 4 but 2^(3) = 8
        $endgroup$
        – Anonymous
        6 mins ago










      • $begingroup$
        This is assuming zero-indexing. So the first element is $n=0$. If you want it to be one-indexed then just subtract 1 from n in the formula.
        $endgroup$
        – Flowers
        3 mins ago













      4












      4








      4





      $begingroup$

      These are just powers of two. So: $2^lfloor n / 2rfloor$






      share|cite|improve this answer









      $endgroup$



      These are just powers of two. So: $2^lfloor n / 2rfloor$







      share|cite|improve this answer












      share|cite|improve this answer



      share|cite|improve this answer










      answered 19 mins ago









      FlowersFlowers

      653410




      653410











      • $begingroup$
        I'm not sure this works for everything, for example the 6th term should be 4 but 2^(3) = 8
        $endgroup$
        – Anonymous
        6 mins ago










      • $begingroup$
        This is assuming zero-indexing. So the first element is $n=0$. If you want it to be one-indexed then just subtract 1 from n in the formula.
        $endgroup$
        – Flowers
        3 mins ago
















      • $begingroup$
        I'm not sure this works for everything, for example the 6th term should be 4 but 2^(3) = 8
        $endgroup$
        – Anonymous
        6 mins ago










      • $begingroup$
        This is assuming zero-indexing. So the first element is $n=0$. If you want it to be one-indexed then just subtract 1 from n in the formula.
        $endgroup$
        – Flowers
        3 mins ago















      $begingroup$
      I'm not sure this works for everything, for example the 6th term should be 4 but 2^(3) = 8
      $endgroup$
      – Anonymous
      6 mins ago




      $begingroup$
      I'm not sure this works for everything, for example the 6th term should be 4 but 2^(3) = 8
      $endgroup$
      – Anonymous
      6 mins ago












      $begingroup$
      This is assuming zero-indexing. So the first element is $n=0$. If you want it to be one-indexed then just subtract 1 from n in the formula.
      $endgroup$
      – Flowers
      3 mins ago




      $begingroup$
      This is assuming zero-indexing. So the first element is $n=0$. If you want it to be one-indexed then just subtract 1 from n in the formula.
      $endgroup$
      – Flowers
      3 mins ago











      1












      $begingroup$

      Alternatively, this is an example of a sequence where the $n$th term is a fixed linear combination of the immediately previous terms: We can write it as
      $$a_n = 2 a_n - 2, qquad a_0 = a_1 = 1.$$
      Using the ansatz $a_n = C r^n$ and substituting in the recursion formula gives $C r^n = 2 C r^n - 2$. Rearranging and clearing gives the characteristic equation $r^2 - 2 = 0$, whose solutions are $pm sqrt2$. So, the general solution is
      $$a_n = A (sqrt2)^n + B(-sqrt2)^n = (sqrt2)^n [A + B(-1)^n] .$$
      Substituting the initial values $a_0 = a_1 = 1$ gives a linear system in the coefficients $A, B$.






      share|cite









      $endgroup$

















        1












        $begingroup$

        Alternatively, this is an example of a sequence where the $n$th term is a fixed linear combination of the immediately previous terms: We can write it as
        $$a_n = 2 a_n - 2, qquad a_0 = a_1 = 1.$$
        Using the ansatz $a_n = C r^n$ and substituting in the recursion formula gives $C r^n = 2 C r^n - 2$. Rearranging and clearing gives the characteristic equation $r^2 - 2 = 0$, whose solutions are $pm sqrt2$. So, the general solution is
        $$a_n = A (sqrt2)^n + B(-sqrt2)^n = (sqrt2)^n [A + B(-1)^n] .$$
        Substituting the initial values $a_0 = a_1 = 1$ gives a linear system in the coefficients $A, B$.






        share|cite









        $endgroup$















          1












          1








          1





          $begingroup$

          Alternatively, this is an example of a sequence where the $n$th term is a fixed linear combination of the immediately previous terms: We can write it as
          $$a_n = 2 a_n - 2, qquad a_0 = a_1 = 1.$$
          Using the ansatz $a_n = C r^n$ and substituting in the recursion formula gives $C r^n = 2 C r^n - 2$. Rearranging and clearing gives the characteristic equation $r^2 - 2 = 0$, whose solutions are $pm sqrt2$. So, the general solution is
          $$a_n = A (sqrt2)^n + B(-sqrt2)^n = (sqrt2)^n [A + B(-1)^n] .$$
          Substituting the initial values $a_0 = a_1 = 1$ gives a linear system in the coefficients $A, B$.






          share|cite









          $endgroup$



          Alternatively, this is an example of a sequence where the $n$th term is a fixed linear combination of the immediately previous terms: We can write it as
          $$a_n = 2 a_n - 2, qquad a_0 = a_1 = 1.$$
          Using the ansatz $a_n = C r^n$ and substituting in the recursion formula gives $C r^n = 2 C r^n - 2$. Rearranging and clearing gives the characteristic equation $r^2 - 2 = 0$, whose solutions are $pm sqrt2$. So, the general solution is
          $$a_n = A (sqrt2)^n + B(-sqrt2)^n = (sqrt2)^n [A + B(-1)^n] .$$
          Substituting the initial values $a_0 = a_1 = 1$ gives a linear system in the coefficients $A, B$.







          share|cite












          share|cite



          share|cite










          answered 3 mins ago









          TravisTravis

          63.8k769151




          63.8k769151





















              0












              $begingroup$

              The sequence is the powers of two, each repeated twice. We can encode the latter feature using the quantity $lfloor fracn2 rfloor$, which has values $0, 0, 1, 1, 2, 2, ldots$.




              So, the sequence is given (for appropriate indexing) by $$color#df0000boxeda_n := 2^lfloor n / 2 rfloor .$$







              share|cite|improve this answer









              $endgroup$

















                0












                $begingroup$

                The sequence is the powers of two, each repeated twice. We can encode the latter feature using the quantity $lfloor fracn2 rfloor$, which has values $0, 0, 1, 1, 2, 2, ldots$.




                So, the sequence is given (for appropriate indexing) by $$color#df0000boxeda_n := 2^lfloor n / 2 rfloor .$$







                share|cite|improve this answer









                $endgroup$















                  0












                  0








                  0





                  $begingroup$

                  The sequence is the powers of two, each repeated twice. We can encode the latter feature using the quantity $lfloor fracn2 rfloor$, which has values $0, 0, 1, 1, 2, 2, ldots$.




                  So, the sequence is given (for appropriate indexing) by $$color#df0000boxeda_n := 2^lfloor n / 2 rfloor .$$







                  share|cite|improve this answer









                  $endgroup$



                  The sequence is the powers of two, each repeated twice. We can encode the latter feature using the quantity $lfloor fracn2 rfloor$, which has values $0, 0, 1, 1, 2, 2, ldots$.




                  So, the sequence is given (for appropriate indexing) by $$color#df0000boxeda_n := 2^lfloor n / 2 rfloor .$$








                  share|cite|improve this answer












                  share|cite|improve this answer



                  share|cite|improve this answer










                  answered 17 mins ago









                  TravisTravis

                  63.8k769151




                  63.8k769151




















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