OFFSET
0,2
LINKS
T. A. Gulliver, Sums of Powers of Integers Divisible by Three, Int. J. Contemp. Math. Sciences, Vol. 7, 2012, no. 38, pp. 1895-1901
Index entries for linear recurrences with constant coefficients, signature (4,-6,4,-1).
FORMULA
a(n) = (3*n*(1+3*n+2*n^2))/2. G.f.: 9*x*(x+1) / (x-1)^4. - Colin Barker, Jul 22 2013
PROG
(PARI) a(n) = sum(k=1, n, (3*k)^2); \\ Michel Marcus, Aug 29 2015
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Dec 22 2012
STATUS
approved