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 A187646 #43 Jul 14 2025 10:13:41
%S A187646 1,1,11,225,6769,269325,13339535,790943153,54631129553,4308105301929,
%T A187646 381922055502195,37600535086859745,4070384057007569521,
%U A187646 480544558742733545125,61445535102359115635655,8459574446076318147830625,1247677142707273537964543265,196258640868140652967646352465
%N A187646 (Signless) Central Stirling numbers of the first kind s(2n,n).
%C A187646 Number of permutations with n cycles on a set of size 2n.
%H A187646 Vincenzo Librandi, <a href="/A187646/b187646.txt">Table of n, a(n) for n = 0..200</a>
%F A187646 Asymptotic: a(n) ~ (2*n/(e*z*(1-z)))^n*sqrt((1-z)/(2*Pi*n*(2z-1))), where z=0.715331862959... is a root of the equation z = 2*(z-1)*log(1-z). - _Vaclav Kotesovec_, May 30 2011
%F A187646 Equivalent: a(n) ~ n!*(2*r^2/(r-1))^n/(2*Pi*n*sqrt(r-2)), where r=A226278. - _Natalia L. Skirrow_, Jul 13 2025
%F A187646 From _Seiichi Manyama_, May 20 2025: (Start)
%F A187646 a(n) = A132393(2*n,n).
%F A187646 a(n) = (2*n)! * [x^(2*n)] (-log(1 - x))^n / n!. (End)
%p A187646 seq(abs(Stirling1(2*n,n)), n=0..20);
%t A187646 Table[Abs[StirlingS1[2n, n]], {n, 0, 12}]
%t A187646 N[1 + 1/(2 LambertW[-1, -Exp[-1/2]/2]), 50] (* The constant z in the asymptotic - _Vladimir Reshetnikov_, Oct 08 2016 *)
%o A187646 (Maxima) makelist(abs(stirling1(2*n,n)),n,0,12);
%o A187646 (PARI) for(n=0,50, print1(abs(stirling(2*n, n, 1)), ", ")) \\ _G. C. Greubel_, Nov 09 2017
%Y A187646 Cf. A008275, A007820, A129505, A132393, A187235, A237993, A242676, A285862.
%K A187646 nonn,easy
%O A187646 0,3
%A A187646 _Emanuele Munarini_, Mar 12 2011