A069975 a(n) = n*(16*n^2-1).

15, 126, 429, 1020, 1995, 3450, 5481, 8184, 11655, 15990, 21285, 27636, 35139, 43890, 53985, 65520, 78591, 93294, 109725, 127980, 148155, 170346, 194649, 221160, 249975, 281190, 314901, 351204, 390195, 431970, 476625, 524256, 574959

Offset

1,1

Links

Table of n, a(n) for n=1..33.

Index entries for linear recurrences with constant coefficients, signature (4,-6,4,-1).

Formula

Sum_{n>=1} 1/a(n) = 3*log(2) - 2 = A016631 - 2. (Ramanujan)

Sum_{n>=1} (-1)^(n+1)/a(n) = 2 - log(2) + sqrt(2)*log(sqrt(2)-1). - Amiram Eldar, Jun 24 2022

Mathematica

Table[n(16n^2-1), {n, 40}] (* Harvey P. Dale, Dec 17 2018 *)

Prog

(PARI) a(n) = n*(16*n^2-1); \\ Michel Marcus, Nov 25 2013

Crossrefs

Cf. A016631.

Sequence in context: A171220 A071080 A193365 * A027779 A337958 A337957

Adjacent sequences: A069972 A069973 A069974 * A069976 A069977 A069978

Keyword

easy,nonn

Author

Benoit Cloitre, Apr 30 2002

Status

approved