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A180846
a(n) = (81^n - 2^n)/79.
6
0, 1, 83, 6727, 544895, 44136511, 3575057423, 289579651327, 23455951757615, 1899932092367071, 153894499481733263, 12465454458020395327, 1009701811099652023535, 81785846699071813910431, 6624653582624816926753103
OFFSET
0,3
COMMENTS
The a(n+1) appear in several triangle sums of Nicomachus's table A036561, i.e., Gi2(4*n), Gi2(4*n+1)/2, Gi2(4*n+2)/4, Gi2(4*n+3)/8 and Gi3(n). See A180662 for information about these giraffe and other chess sums.
FORMULA
a(n) = (81^n - 2^n)/79.
G.f.: x/((81*x-1)*(2*x-1)).
MATHEMATICA
Table[(81^n-2^n)/79, {n, 0, 15}] (* Vladimir Joseph Stephan Orlovsky, Apr 13 2011 *)
PROG
(Magma) [(81^n-2^n)/79: n in [0..50]]; // Vincenzo Librandi, Apr 15 2011
KEYWORD
easy,nonn
AUTHOR
Johannes W. Meijer, Sep 21 2010
STATUS
approved