This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A377339 #20 Oct 26 2024 14:46:24
%S A377339 1,2,4,20,144,1332,15920,225332,3758272,71711540,1544139216,
%T A377339 37040248500,979378764320,28308318200372,887957701803952,
%U A377339 30043664101434164,1090686549233837952,42290355849577306932,1744321111108101722768,76261355010301941319604
%N A377339 E.g.f. satisfies A(x) = ( 1 + (exp(x*A(x)) - 1)/A(x) )^2.
%F A377339 E.g.f.: B(x)^2, where B(x) is the e.g.f. of A377347.
%F A377339 a(n) = 2 * Sum_{k=0..floor((2*n+2)/3)} (2*n-2*k+1)!/(2*n-3*k+2)! * Stirling2(n,k).
%o A377339 (PARI) a(n) = 2*sum(k=0, (2*n+2)\3, (2*n-2*k+1)!/(2*n-3*k+2)!*stirling(n, k, 2));
%Y A377339 Cf. A377326, A377340.
%Y A377339 Cf. A377347.
%K A377339 nonn
%O A377339 0,2
%A A377339 _Seiichi Manyama_, Oct 26 2024