OFFSET
0,2
LINKS
Bruno Berselli, Table of n, a(n) for n = 0..1000
Index entries for linear recurrences with constant coefficients, signature (3,-3,1).
FORMULA
O.g.f.: 1-x*(23+17*x+2*x^2)/(-1+x)^3. - R. J. Mathar, Apr 12 2008
E.g.f.: (21*x*(x+1)+2)*e^x-1. - Gopinath A. R., Feb 13 2012
Sum_{n>=0} 1/a(n) = 3/4+sqrt(42)/84*Pi*coth( Pi*sqrt(42)/21) = 1.0738233857899... - R. J. Mathar, May 07 2024
MAPLE
MATHEMATICA
Join[{1}, 21 Range[41]^2 + 2] (* Bruno Berselli, Feb 06 2012 *)
Join[{1}, LinearRecurrence[{3, -3, 1}, {23, 86, 191}, 50]] (* Vincenzo Librandi, Aug 03 2015 *)
PROG
(Magma) [1] cat [21*n^2+2: n in [1..50]]; // Vincenzo Librandi, Aug 03 2015
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
STATUS
approved