OFFSET
0,2
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..1500
Eric Weisstein's World of Mathematics, Pentagonal Pyramidal Number
Index entries for linear recurrences with constant coefficients, signature (1,0,6,-6,0,-15,15,0,20,-20,0,-15,15,0,6,-6,0,-1,1).
FORMULA
G.f.: -4*x*(x^16 +143*x^15 +481*x^14 +1394*x^13 +9661*x^12 +10814*x^11 +15996*x^10 +45222*x^9 +25248*x^8 +23414*x^7 +33610*x^6 +9218*x^5 +5203*x^4 +3515*x^3 +319*x^2 +72*x +9)/((x -1)^7*(x^2 +x +1)^6). [Colin Barker, Nov 16 2012]
a(n) = A015224(n)^2. - R. J. Mathar, Jul 30 2016
MATHEMATICA
Select[CoefficientList[Series[(x(2x+1))/(x-1)^4, {x, 0, 50}], x], EvenQ]^2 (* Harvey P. Dale, Feb 27 2012 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
STATUS
approved