A375826 E.g.f. satisfies A(x) = 1/(1 - x*A(x))^(x^2).
1, 0, 0, 6, 12, 40, 1260, 11088, 99120, 1926720, 32800320, 535328640, 11274642720, 259872088320, 6108539621184, 158608655251200, 4495317057504000, 134114095312404480, 4253953999500357120, 143971794376985272320, 5141239842495675340800
Offset: 0
Keywords
Programs
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PARI
a(n) = n!*sum(k=0, n\3, (n-2*k+1)^(k-1)*abs(stirling(n-2*k, k, 1))/(n-2*k)!);
Formula
a(n) = n! * Sum_{k=0..floor(n/3)} (n-2*k+1)^(k-1) * |Stirling1(n-2*k,k)|/(n-2*k)!.