OFFSET
0,2
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..1000
MATHEMATICA
(* r = A000081 *) r[n_] := r[n] = If[n<2, n, Sum[DivisorSum[j, #*r[#]&] * r[n-j], {j, 1, n-1}]/(n-1)]; b[n_] := b[n] = -If[n<0, 1, Sum[b[n-i] * r[i+1], {i, 1, n+1}]]; B[n_] := Sum[b[i]*x^i, {i, 0, n}]; T[n_, k_] := Coefficient[B[n]^k, x, n-k]; a[n_] := T[n+2, 2]; Table[a[n], {n, 0, 30}] (* Jean-François Alcover, Mar 23 2017, after Alois P. Heinz *)
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved