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A329289
G.f.: (1 + x) * (1 + x^2) * Product_{k>=1} (1 + x^k).
1
1, 2, 3, 5, 6, 8, 11, 14, 18, 23, 29, 36, 45, 55, 67, 82, 99, 119, 143, 170, 202, 240, 283, 333, 391, 457, 533, 621, 721, 835, 966, 1114, 1282, 1474, 1690, 1935, 2213, 2525, 2877, 3274, 3719, 4219, 4781, 5409, 6112, 6900, 7778, 8758, 9852, 11068, 12422
OFFSET
0,2
COMMENTS
Number of partitions of n into distinct parts if there are two types of 1's and two types of 2's.
FORMULA
a(n) = A036469(n) - A036469(n-4).
a(n) ~ exp(Pi*sqrt(n/3)) / (3^(1/4)*n^(3/4)). - Vaclav Kotesovec, Jun 11 2020
MATHEMATICA
nmax = 50; CoefficientList[Series[(1 + x) (1 + x^2) Product[(1 + x^k), {k, 1, nmax}], {x, 0, nmax}], x]
a[0] = 1; a[n_] := a[n] = (1/n) Sum[Sum[(-1)^(k/d + 1) If[d < 3, 2, 1] d, {d, Divisors[k]}] a[n - k], {k, 1, n}]; Table[a[n], {n, 0, 50}]
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Jun 07 2020
STATUS
approved