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A220443 a(n) = Sum_{i=1..n} (3i)^2. 1
0, 9, 45, 126, 270, 495, 819, 1260, 1836, 2565, 3465, 4554, 5850, 7371, 9135, 11160, 13464, 16065, 18981, 22230, 25830, 29799, 34155, 38916, 44100, 49725, 55809, 62370, 69426, 76995, 85095, 93744, 102960, 112761, 123165, 134190, 145854, 158175, 171171, 184860, 199260 (list; graph; refs; listen; history; text; internal format)
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
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
a(n) = A045943(n) * A005408(n). - Bruce J. Nicholson, Jun 12 2020
PROG
(PARI) a(n) = sum(k=1, n, (3*k)^2); \\ Michel Marcus, Aug 29 2015
CROSSREFS
Equals 9*A000330.
Sequence in context: A068314 A152996 A188351 * A289721 A060008 A212089
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Dec 22 2012
STATUS
approved

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Last modified February 23 17:37 EST 2024. Contains 370283 sequences. (Running on oeis4.)