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A329466
Expansion of Sum_{k>=1} (-1 + Product_{j>=1} (1 + x^(k*j*(j + 1)/2))).
1
1, 1, 2, 2, 1, 3, 2, 2, 3, 3, 2, 4, 2, 3, 3, 4, 2, 5, 3, 5, 5, 4, 1, 6, 4, 3, 4, 7, 3, 7, 5, 7, 3, 5, 5, 8, 5, 6, 6, 8, 3, 10, 4, 7, 8, 7, 5, 10, 7, 10, 5, 10, 6, 9, 9, 13, 7, 8, 6, 14, 7, 10, 10, 14, 9, 12, 9, 12, 7, 17, 8, 14, 10, 14, 12, 17, 12, 12, 10, 20
OFFSET
1,3
COMMENTS
Inverse Moebius transform of A024940.
FORMULA
G.f.: Sum_{k>=1} A024940(k) * x^k / (1 - x^k).
a(n) = Sum_{d|n} A024940(d).
MATHEMATICA
nmax = 80; CoefficientList[Series[Sum[-1 + Product[(1 + x^(k j (j + 1)/2)), {j, 1, nmax}], {k, 1, nmax}], {x, 0, nmax}], x] // Rest
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Nov 13 2019
STATUS
approved