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A327940 Expansion of e.g.f. exp(Sum_{i>=1} Sum_{j=1..i-1} x^(i*j) / (i*j)). 1
1, 0, 1, 2, 9, 44, 385, 1854, 23233, 153656, 2151441, 18787130, 338487721, 3165541092, 60609811249, 835202858294, 14913805143105, 228441779869424, 5319673396479073, 81040768940877426, 2153026504862728201, 39759334398324543260, 988919906784578473761 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

LINKS

Table of n, a(n) for n=0..22.

FORMULA

E.g.f.: exp(Sum_{k>=1} floor(A000005(k)/2) * x^k / k).

E.g.f.: exp(Sum_{k>=1} A056924(k) * x^k / k).

E.g.f.: Product_{k>=1} 1 / (1 - x^A026424(k))^(1/A026424(k)).

MATHEMATICA

nmax = 22; CoefficientList[Series[Exp[Sum[Floor[DivisorSigma[0, k]/2] x^k/k, {k, 1, nmax}]], {x, 0, nmax}], x] Range[0, nmax]!

a[n_] := a[n] = If[n == 0, 1, Sum[Floor[DivisorSigma[0, k]/2] a[n - k], {k, 1, n}]/n]; Table[n! a[n], {n, 0, 22}]

CROSSREFS

Cf. A000005, A026424, A028342, A056924, A206303, A327927.

Sequence in context: A073478 A322613 A318913 * A088369 A303938 A059388

Adjacent sequences:  A327937 A327938 A327939 * A327941 A327942 A327943

KEYWORD

nonn

AUTHOR

Ilya Gutkovskiy, Sep 30 2019

STATUS

approved

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Last modified April 1 14:52 EDT 2020. Contains 333163 sequences. (Running on oeis4.)