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%I #4 Nov 27 2019 12:52:47
%S 1,1,3,6,16,21,102,109,565,826,4913,4924,28036,28049,378218,427646,
%T 1841532,1841549,29704312,29704331,182590131,194454702,3660242371,
%U 3660242394,17058569521,17059419626,308650641577,311298706504,1436650115240,1436650115269
%N a(1) = 1; a(n+1) = Sum_{d|n} binomial(n,d) * a(d).
%t a[n_] := a[n] = Sum[Binomial[n - 1, d] a[d], {d, Divisors[n - 1]}]; a[1] = 1; Table[a[n], {n, 1, 30}]
%Y Cf. A003238, A056045.
%K nonn
%O 1,3
%A _Ilya Gutkovskiy_, Nov 27 2019