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A185395
a(3n) = n^2, a(3n+1) = a(3n+2) = 3*n*(n+1)/2.
4
0, 0, 0, 1, 3, 3, 4, 9, 9, 9, 18, 18, 16, 30, 30, 25, 45, 45, 36, 63, 63, 49, 84, 84, 64, 108, 108, 81, 135, 135, 100, 165, 165, 121, 198, 198, 144, 234, 234, 169, 273, 273, 196, 315, 315, 225, 360, 360, 256
OFFSET
0,5
COMMENTS
Expansion of ((x+x^2)/(1-x^3))^k with k = 3 ; for k = 1 see A011655, for k = 2 see A186731, for k = 4 see A185292.
Column k = 3 of triangle in A198295.
FORMULA
G.f.: (x*(1+x)/(1-x^3))^3.
MATHEMATICA
LinearRecurrence[{0, 0, 3, 0, 0, -3, 0, 0, 1}, {0, 0, 0, 1, 3, 3, 4, 9, 9}, 50] (* Harvey P. Dale, Jan 23 2013 *)
PROG
(PARI) x='x+O('x^50); concat([0, 0, 0], Vec((x*(1+x)/(1-x^3))^3)) \\ G. C. Greubel, Jun 29 2017
KEYWORD
easy,nonn
AUTHOR
Philippe Deléham, Jan 21 2012
STATUS
approved