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A181082
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Expansion of g.f.: exp( Sum_{n>=1} [Sum_{k=0..n} C(n,k)^(n+k) * x^k] * x^n/n ).
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4
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1, 1, 2, 6, 34, 375, 15200, 2066401, 450054919, 199271253643, 431399012916702, 2151987403947457136, 15451465958263071713102, 331187643758039140349444047, 33475597220485400781283541412048
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OFFSET
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0,3
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COMMENTS
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Conjecture: this sequence consists entirely of integers.
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LINKS
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EXAMPLE
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G.f.: A(x) = 1 + x + 2*x^2 + 6*x^3 + 34*x^4 + 375*x^5 + 15200*x^6 +...
The logarithm of g.f. A(x) begins:
log(A(x)) = x + 3*x^2/2 + 13*x^3/3 + 111*x^4/4 + 1686*x^5/5 + 88737*x^6/6 + ... + A181083(n)*x^n/n + ...
and equals the series:
log(A(x)) = (1 + x)*x + (1 + 2^3*x + x^2)*x^2/2
+ (1 + 3^4*x + 3^5*x^2 + x^3)*x^3/3
+ (1 + 4^5*x + 6^6*x^2 + 4^7*x^3 + x^4)*x^4/4
+ (1 + 5^6*x + 10^7*x^2 + 10^8*x^3 + 5^9*x^4 + x^5)*x^5/5
+ (1 + 6^7*x + 15^8*x^2 + 20^9*x^3 + 15^10*x^4 + 6^11*x^5 + x^6)*x^6/6 + ...
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MATHEMATICA
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With[{m=20}, CoefficientList[Series[Exp[Sum[Sum[Binomial[n, k]^(n+k)*x^(n+k)/n, {k, 0, n}], {n, m+1}]], {x, 0, m}], x]] (* G. C. Greubel, Apr 05 2021 *)
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PROG
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(PARI) {a(n)=polcoeff(exp(sum(m=1, n, sum(k=0, m, binomial(m, k)^(m+k)*x^k)*x^m/m)+x*O(x^n)), n)}
(Magma)
m:=20;
R<x>:=PowerSeriesRing(Integers(), m);
Coefficients(R!( Exp( (&+[ (&+[ Binomial(n, k)^(n+k)*x^(n+k)/n : k in [0..n]]): n in [1..m+1]]) ) )); // G. C. Greubel, Apr 05 2021
(Sage)
m=20;
P.<x> = PowerSeriesRing(ZZ, prec)
return P( exp( sum( sum( binomial(n, k)^(n+k)*x^(n+k)/n for k in (0..n) ) for n in (1..m+1)) ) ).list()
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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