OFFSET
1,1
COMMENTS
Intersection of A000217 and A033991 (even hexagonal numbers divided by 2). - Michel Marcus, Jun 20 2015
LINKS
Colin Barker, Table of n, a(n) for n = 1..327
Index entries for linear recurrences with constant coefficients, signature (1155,-1155,1).
FORMULA
G.f.: -3*x*(35*x+1) / ((x-1)*(x^2-1154*x+1)).
EXAMPLE
3 is in the sequence because 3 is the 2nd triangular number, and 2*3 is the 2nd hexagonal number.
MATHEMATICA
LinearRecurrence[{1155, -1155, 1}, {3, 3570, 4119885}, 20] (* Vincenzo Librandi, Jun 20 2015 *)
PROG
(PARI) Vec(-3*x*(35*x+1)/((x-1)*(x^2-1154*x+1)) + O(x^20))
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Colin Barker, Jun 19 2015
STATUS
approved