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%I #12 Dec 15 2017 07:27:14
%S 1,2,3,6,11,26,58,142,351,890,2282,5948,15624,41442,110703,297676,
%T 804892,2187490,5971392,16366734,45021391,124253828,343956858,
%U 954760502,2656946827,7411140120,20716895918,58027609028,162837485745
%N Expansion of square of g.f. for A051573.
%H G. C. Greubel, <a href="/A051603/b051603.txt">Table of n, a(n) for n = 0..1000</a>
%t (* 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_ *)
%Y Cf. A052250, A051573.
%K nonn
%O 0,2
%A _David Broadhurst_
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