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A180845
a(n) = (16^n-3^n)/13
6
0, 1, 19, 313, 5035, 80641, 1290499, 20648713, 330381595, 5286112081, 84577812979, 1353245066713, 21651921244555, 346430740444321, 5542891848703459, 88686269584038313, 1418980313358961915
OFFSET
0,3
COMMENTS
The a(n+1) appear in several triangle sums of Nicomachus' table A036561, i.e Gi1(4*n), Gi1(4*n+1)/2, Gi1(4*n+2)/4, Gi1(4*n+3)/8 and Gi4(n). See A180662 for information about these giraffe and other chess sums.
FORMULA
a(n) = (16^n-3^n)/13
G.f.: x/((16*x-1)*(3*x-1))
MATHEMATICA
Table[(16^n-3^n)/13, {n, 0, 30}] (* Vladimir Joseph Stephan Orlovsky, Feb 15 2011*)
KEYWORD
easy,nonn
AUTHOR
Johannes W. Meijer, Sep 21 2010
STATUS
approved