A331404 a(0) = 1; a(n) = Sum_{k=1..n} (-1)^(n - k) * binomial(n,k) * a(k-1) * a(n-k).
1, 1, -1, -7, 19, 229, -1009, -17263, 105211, 2332141, -18148681, -494079367, 4678377859, 151026527989, -1684778524129, -62909200846303, 807879476432971, 34252260613710781, -497629527847938361, -23615390533271153527, 382915997208515638099, 20108383384185058286149
Offset: 0
Keywords
Programs
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Mathematica
a[n_] := a[n] = Sum[(-1)^(n - k) Binomial[n, k] a[k - 1] a[n - k], {k, 1, n}]; a[0] = 1; Table[a[n], {n, 0, 21}] -
PARI
seq(n)={my(a=vector(n+1)); a[1]=1; for(n=1, #a-1, a[1+n]=sum(k=1,n, (-1)^(n - k) * binomial(n,k) * a[k] * a[1+n-k])); a} \\ Andrew Howroyd, Jan 16 2020
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