A337547 Number of compositions (ordered partitions) of n into distinct parts congruent to 1 mod 3.
1, 1, 0, 0, 1, 2, 0, 1, 2, 0, 1, 4, 6, 1, 4, 6, 1, 6, 12, 1, 6, 18, 25, 8, 24, 25, 8, 30, 49, 10, 42, 73, 10, 48, 121, 132, 60, 145, 132, 72, 217, 254, 84, 265, 374, 96, 361, 616, 114, 433, 856, 846, 553, 1218, 864, 649, 1578, 1602, 817, 2180, 2340, 937, 2780, 3798, 1129, 3622
Offset: 0
Keywords
Examples
a(12) = 6 because we have [7, 4, 1], [7, 1, 4], [4, 7, 1], [4, 1, 7], [1, 7, 4] and [1, 4, 7].
Programs
-
Mathematica
nmax = 65; CoefficientList[Series[Sum[k! x^(k (3 k - 1)/2)/Product[1 - x^(3 j), {j, 1, k}], {k, 0, nmax}], {x, 0, nmax}], x]
Formula
G.f.: Sum_{k>=0} k! * x^(k*(3*k - 1)/2) / Product_{j=1..k} (1 - x^(3*j)).