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A074610
a(n) = 3^n + 9^n.
3
2, 12, 90, 756, 6642, 59292, 532170, 4785156, 43053282, 387440172, 3486843450, 31381236756, 282430067922, 2541867422652, 22876797237930, 205891146443556, 1853020231898562, 16677181828806732, 150094635684419610
OFFSET
0,1
FORMULA
From Mohammad K. Azarian, Jan 11 2009: (Start)
G.f.: 1/(1-3*x) + 1/(1-9*x).
E.g.f.: exp(3*x) + exp(9*x). (End)
a(n) = 12*a(n-1) - 27*a(n-2) with a(0)=2, a(1)=12. - Vincenzo Librandi, Jul 21 2010
a(n) = 2*A025551(n). - G. C. Greubel, Jan 13 2024
MATHEMATICA
Table[3^n + 9^n, {n, 0, 25}]
LinearRecurrence[{12, -27}, {2, 12}, 20] (* Harvey P. Dale, May 18 2023 *)
PROG
(Magma) [3^n+9^n: n in [0..30]]; // G. C. Greubel, Jan 13 2024
(SageMath) [3^n+9^n for n in range(31)] # G. C. Greubel, Jan 13 2024
KEYWORD
easy,nonn
AUTHOR
Robert G. Wilson v, Aug 25 2002
STATUS
approved