OFFSET
0,2
FORMULA
From Daniel Forgues, May 03 2011: (Start)
If 0 <= n <= 3 then a(n) = 2 T_n, otherwise a(n) = 2 (T_n - t_{n-1}), where T_n is the n-th tetrahedral number, t_n the n-th triangular number.
G.f.: (2*x*(1 - 6*x^3 + 14*x^4 - 11*x^5 + 3*x^6))/(1 - x)^4, n >= 0.
(End)
a(n) = n*(n^2+5)/3 + (4*n-6)*A171386(n). - Omar E. Pol, Aug 14 2013
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Omar E. Pol, Jul 07 2009, Jul 13 2009
EXTENSIONS
Edited by N. J. A. Sloane, Jul 18 2009
STATUS
approved