OFFSET
0,2
COMMENTS
Sum of the numbers from 3*(n-1) to 3*(n+1). - Bruno Berselli, Oct 25 2018
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..1000
Tanya Khovanova, Recursive Sequences
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 333
Index entries for linear recurrences with constant coefficients, signature (2, -1).
FORMULA
G.f.: 21*x/(x-1)^2. - Vincenzo Librandi, Jun 10 2013
MATHEMATICA
Range[0, 1500, 21] (* Vladimir Joseph Stephan Orlovsky, Jun 01 2011 *)
CoefficientList[Series[21 x / (x - 1)^2, {x, 0, 60}], x] (* Vincenzo Librandi, Jun 10 2013 *)
PROG
(PARI) a(n)=21*n \\ Charles R Greathouse IV, Oct 07 2015
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
STATUS
approved