A120353 Sum of 5 consecutive powers of 3, starting with a power of 9.
121, 1089, 9801, 88209, 793881, 7144929, 64304361, 578739249, 5208653241, 46877879169, 421900912521, 3797108212689, 34173973914201, 307565765227809, 2768091887050281, 24912826983452529, 224215442851072761, 2017938985659654849, 18161450870936893641
Offset: 1
Examples
a(2) = 3^2 + 3^3 + 3^4 + 3^5 + 3^6 = 121*(3^2) = 1089.
Links
- Vincenzo Librandi, Table of n, a(n) for n = 1..300
- Tanya Khovanova, Recursive Sequences
- Index entries for linear recurrences with constant coefficients, signature (9).
Programs
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Magma
[121*3^(2*n-2): n in [1..30]]; // Vincenzo Librandi, Jun 10 2011
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Mathematica
Total/@Select[Partition[3^Range[0,60],5,1],IntegerQ[Log[9, First[#]]]&] (* or *) Table[121 3^(2n-2),{n,30}] (* Harvey P. Dale, May 03 2011 *) -
PARI
a(n)=121*9^(n-1) \\ Charles R Greathouse IV, Jul 11 2016
Formula
a(n) = 121*3^(2n-2).
Extensions
Corrected and extended by Harvey P. Dale, May 03 2011
Comments