A383207 Expansion of e.g.f. (exp(f(x)) - 1)^2 / 2, where f(x) = (exp(2*x) - 1)/2.
0, 0, 1, 9, 71, 575, 4957, 45829, 454015, 4804191, 54094749, 645720757, 8142419727, 108110708511, 1506969153757, 21993472779461, 335257957315199, 5325979566073919, 87999598425114045, 1509471498829147637, 26835040585117438415, 493677094649876461759, 9384926300821643459133
Offset: 0
Keywords
Programs
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PARI
a(n) = sum(k=2, n, 2^(n-k)*stirling(n, k, 2)*stirling(k, 2, 2));
Formula
a(n) = Sum_{k=2..n} 2^(n-k) * Stirling2(n,k) * Stirling2(k,2).