Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #8 Apr 06 2021 04:54:51
%S 1,1,2,10,92,1367,87090,20385333,6633475836,4096297538926,
%T 14834973644512627,119919823546238898903,1273371038284317852447990,
%U 41086272137585936052959008420,6982122140549374036504235218052104
%N Expansion of g.f.: exp( Sum_{n>=1} [Sum_{k=0..n} binomial(n,k)^(n+k+1) * x^k] * x^n/n ).
%C Conjecture: this sequence consists entirely of integers.
%H G. C. Greubel, <a href="/A181084/b181084.txt">Table of n, a(n) for n = 0..70</a>
%e G.f.: A(x) = 1 + x + 2*x^2 + 10*x^3 + 92*x^4 + 1367*x^5 + 87090*x^6 + ...
%e The logarithm of g.f. A(x) begins:
%e log(A(x)) = x + 3*x^2/2 + 25*x^3/3 + 327*x^4/4 + 6336*x^5/5 + 513657*x^6/6 + ... + A181085(n)*x^n/n + ...
%e and equals the series:
%e log(A(x)) = (1 + x)*x + (1 + 2^4*x + x^2)*x^2/2
%e + (1 + 3^5*x + 3^6*x^2 + x^3)*x^3/3
%e + (1 + 4^6*x + 6^7*x^2 + 4^8*x^3 + x^4)*x^4/4
%e + (1 + 5^7*x + 10^8*x^2 + 10^9*x^3 + 5^10*x^4 + x^5)*x^5/5
%e + (1 + 6^8*x + 15^9*x^2 + 20^10*x^3 + 15^11*x^4 + 6^12*x^5 + x^6)*x^6/6 + ...
%t With[{m=20}, CoefficientList[Series[Exp[Sum[Sum[Binomial[n, k]^(n+k+1)*x^(n+k)/n, {k,0,n}], {n, m+1}]], {x,0,m}], x]] (* _G. C. Greubel_, Apr 05 2021 *)
%o (PARI) {a(n)=polcoeff(exp(sum(m=1, n, sum(k=0, m, binomial(m,k)^(m+k+1)*x^k)*x^m/m) + x*O(x^n)), n)}
%o (Magma)
%o m:=20;
%o R<x>:=PowerSeriesRing(Integers(), m);
%o Coefficients(R!( Exp( (&+[ (&+[ Binomial(n,k)^(n+k+1)*x^(n+k)/n : k in [0..n]]): n in [1..m+1]]) ) )); // _G. C. Greubel_, Apr 05 2021
%o (Sage)
%o m=20;
%o def A181084_list(prec):
%o P.<x> = PowerSeriesRing(ZZ, prec)
%o return P( exp( sum( sum( binomial(n,k)^(n+k+1)*x^(n+k)/n for k in (0..n) ) for n in (1..m+1)) ) ).list()
%o A181084_list(m) # _G. C. Greubel_, Apr 05 2021
%Y Cf. A181085 (log), variants: A181080, A181082.
%K nonn
%O 0,3
%A _Paul D. Hanna_, Oct 28 2010