A370747 Number of partitions of n into distinct parts such that number of parts is a multiples of 3.
1, 0, 0, 0, 0, 0, 1, 1, 2, 3, 4, 5, 7, 8, 10, 12, 14, 16, 19, 21, 24, 28, 31, 35, 40, 45, 51, 59, 66, 76, 87, 100, 114, 133, 151, 175, 201, 232, 265, 307, 349, 402, 458, 524, 594, 680, 767, 872, 983, 1112, 1248, 1409, 1575, 1770, 1976, 2211, 2460, 2748, 3048, 3393, 3759, 4173, 4612, 5112
Offset: 0
Keywords
Examples
a(12) = 7 counts these partitions: 921, 831, 741, 732, 651, 642, 543.
Programs
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PARI
my(N=70, x='x+O('x^N)); Vec(sum(k=0, N, prod(j=1, 3*k, x^j/(1-x^j))))
Formula
G.f.: Sum_{k>=0} x^(3*k*(3*k+1)/2) / Product_{j=1..3*k} (1-x^j) = Sum_{k>=0} Product_{j=1..3*k} (x^j/(1-x^j)).