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a(n) = Fibonacci(7^n).
7

%I #35 Oct 02 2024 07:53:51

%S 1,13,7778742049,

%T 215414832505658809004682396169711233230800418578767753330908886771798637

%N a(n) = Fibonacci(7^n).

%H Seiichi Manyama, <a href="/A145234/b145234.txt">Table of n, a(n) for n = 0..4</a>

%F a(n) = (G^(7^n) - (1 - G)^(7^n))/sqrt(5) where G = (1 + sqrt(5))/2.

%F a(n) = (2/sqrt(5))*cosh(7^n*arccosh(sqrt(5)/2)).

%F a(n+1) = 125*a(n)^7 - 175*a(n)^5 + 70*a(n)^3 - 7*a(n) with a(0) = 1. - _Peter Bala_, Nov 25 2022

%p A145234 := proc(n) combinat[fibonacci](7^n) ; end proc:

%p seq(A145234(n),n=1..3) ; # _R. J. Mathar_, Apr 01 2011

%t G = (1 + Sqrt[5])/2; Table[Expand[(G^(7^n) - (1 - G)^(7^n))/Sqrt[5]], {n, 1, 6}]

%t (* Second program: *)

%t Table[Round[N[(2/Sqrt[5])*Cosh[7^n*ArcCosh[Sqrt[5]/2]], 1000]], {n, 1, 4}]

%o (Magma) [Fibonacci(7^n): n in [0..5]]; // _Vincenzo Librandi_, Apr 02 2011

%Y Cf. A000045.

%Y Cf. (k^n)-th Fibonacci number: A058635 (k=2), A045529 (k=3), A145231 (k=4), A145232 (k=5), A145233 (k=6), this sequence (k=7), A250487 (k=8), A250488 (k=9), A250489 (k=10).

%K nonn,easy

%O 0,2

%A _Artur Jasinski_, Oct 05 2008