OFFSET
1,2
COMMENTS
Also the index of the first of two consecutive pentagonal numbers whose sum is also a pentagonal number. - Colin Barker, Dec 22 2014
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..200
Index entries for linear recurrences with constant coefficients, signature (1,1154,-1154,-1,1).
MATHEMATICA
CoefficientList[Series[x (3 x^3 + 145 x^2 - 507 x - 25)/((x - 1) (x^2 - 34 x + 1) (x^2 + 34 x + 1)), {x, 0, 20}], x] (* Vincenzo Librandi, Oct 20 2014 *)
PROG
(PARI) concat(0, Vec(x^2*(3*x^3+145*x^2-507*x-25)/((x-1)*(x^2-34*x+1)*(x^2+34*x+1)) + O(x^20))) \\ Colin Barker, Oct 20 2014
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Richard Choulet, Sep 26 2008
EXTENSIONS
a(6) corrected, and more terms from Colin Barker, Oct 20 2014
Edited, name changed by Colin Barker, Oct 20 2014
STATUS
approved