OFFSET
0,3
LINKS
OEIS Wiki, Figurate numbers
Eric Weisstein's World of Mathematics, Pyramidal Number
Index entries for linear recurrences with constant coefficients, signature (-3,-2,2,3,1).
FORMULA
G.f.: x*(1 - 6*x)/((x - 1)*(x + 1)^4).
a(n) = (-1)^n*(2*n - 1)*(14*n^2 + 34*n + 15)/48 + 5/16.
a(n) = Sum_{k = 0..n} (-1)^k*A007584(k).
MATHEMATICA
Table[(-1)^n (2 n - 1) ((14 n^2 + 34 n + 15)/48) + 5/16, {n, 0, 40}]
LinearRecurrence[{-3, -2, 2, 3, 1}, {0, -1, 9, -25, 55}, 41]
CROSSREFS
KEYWORD
sign,easy
AUTHOR
Ilya Gutkovskiy, Feb 26 2016
STATUS
approved