A375561 Expansion of e.g.f. 1 / (1 + x * log(1 - x^2)).
1, 0, 0, 6, 0, 60, 720, 1680, 40320, 453600, 3326400, 67858560, 878169600, 11935123200, 240708948480, 3946374432000, 73927190937600, 1621341859737600, 32960791774310400, 758085507686707200, 18570669277095936000, 454016684061997056000, 12100759898595611443200
Offset: 0
Keywords
Programs
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PARI
my(N=30, x='x+O('x^N)); Vec(serlaplace(1/(1+x*log(1-x^2)))) -
PARI
a(n) = n!*sum(k=0, n\2, (n-2*k)!*abs(stirling(k, n-2*k, 1))/k!);
Formula
a(n) = n! * Sum_{k=0..floor(n/2)} (n-2*k)! * |Stirling1(k,n-2*k)|/k!.