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A353184 Expansion of e.g.f. 1/(1 - Sum_{k>=1} x^(k^2) / (k^2)). 2
1, 1, 2, 6, 30, 180, 1260, 10080, 93240, 1015560, 12146400, 158004000, 2226193200, 34162128000, 565750785600, 10034584560000, 190820565936000, 3845407181616000, 81995523626016000, 1844123531009760000, 43689721287532320000, 1086745683839175360000 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,3
LINKS
FORMULA
a(0) = 1; a(n) = Sum_{k=1..floor(sqrt(n))} (k^2-1)! * binomial(n,k^2) * a(n-k^2).
MATHEMATICA
a[0] = 1; a[n_] := a[n] = Sum[(k^2 - 1)! * Binomial[n, k^2] * a[n - k^2], {k, 1, Floor@Sqrt[n]}]; Array[a, 22, 0] (* Amiram Eldar, Apr 30 2022 *)
PROG
(PARI) my(N=30, x='x+O('x^N)); Vec(serlaplace(1/(1-sum(k=1, sqrtint(N), x^k^2/(k^2)))))
(PARI) a_vector(n) = my(v=vector(n+1)); v[1]=1; for(i=1, n, v[i+1]=sum(j=1, sqrtint(i), (j^2-1)!*binomial(i, j^2)*v[i-j^2+1])); v;
CROSSREFS
Sequence in context: A180895 A180896 A180897 * A096769 A365975 A111059
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Apr 29 2022
STATUS
approved

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Last modified February 23 11:05 EST 2024. Contains 370283 sequences. (Running on oeis4.)