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 A221955 #54 Sep 21 2024 19:14:26
%S A221955 1,12,432,25920,2177280,235146240,31039303680,4842131374080,
%T A221955 871583647334400,177803064056217600,40539098604817612800,
%U A221955 10215852848414038425600,2819575386162274605465600,845872615848682381639680000,274062727534973091651256320000,95373829182170635894637199360000,35479064455767476552805038161920000
%N A221955 a(n) = 6^(n-1) * n! * Catalan(n-1).
%C A221955 a(n+1) is the number of square roots of any permutation in S_{24*n} whose disjoint cycle decomposition consists of 2*n cycles of length 12. - _Luis Manuel Rivera Martínez_, Feb 28 2015
%H A221955 Vincenzo Librandi, <a href="/A221955/b221955.txt">Table of n, a(n) for n = 1..200</a>
%H A221955 W. van der Aalst, J. Buijs and B. van Dongen, <a href="https://hal.inria.fr/hal-01515548">Towards Improving the Representational Bias of Process Mining</a>, 2012.
%H A221955 Jesús Leaños, Rutilo Moreno and Luis Manuel Rivera-Martínez, <a href="http://ajc.maths.uq.edu.au/pdf/52/ajc_v52_p041.pdf">On the number of mth roots of permutations</a>, Australas. J. Combin., Vol. 52 (2012), pp. 41-54 (Theorem 1).
%F A221955 a(n) = 12*(2*n-3)*a(n-1) with a(1)=1. - _Bruno Berselli_, Mar 11 2013
%F A221955 E.g.f.: (1-sqrt(1-24*x))/12. - _Luis Manuel Rivera Martínez_, Mar 04 2015
%F A221955 a(1) = 1; a(n) = 6 * Sum_{k=1..n-1} binomial(n,k) * a(k) * a(n-k). - _Ilya Gutkovskiy_, Jul 10 2020
%F A221955 From _Amiram Eldar_, Jan 08 2022: (Start)
%F A221955 Sum_{n>=1} 1/a(n) = 1 + e^(1/24)*sqrt(Pi)*erf(1/(2*sqrt(6)))/(2*sqrt(6)), where erf is the error function.
%F A221955 Sum_{n>=1} (-1)^(n+1)/a(n) = 1 - e^(-1/24)*sqrt(Pi)*erfi(1/(2*sqrt(6)))/(2*sqrt(6)), where erfi is the imaginary error function. (End)
%p A221955 A221955:= n-> 3*6^(n-2)*n!*binomial(2*n,n)/(2*n-1); seq(A221955(n), n=1..30); # _G. C. Greubel_, Apr 02 2021
%t A221955 Table[CatalanNumber[n-1] 6^(n-1) n!, {n, 20}] (* _Vincenzo Librandi_, Mar 11 2013 *)
%t A221955 nxt[{n_,a_}]:={n+1,12a(2n-1)}; NestList[nxt,{1,1},20][[;;,2]] (* _Harvey P. Dale_, Sep 21 2024 *)
%o A221955 (Magma) [Catalan(n-1)*6^(n-1)*Factorial(n): n in [1..20]]; // _Vincenzo Librandi_, Mar 11 2013
%o A221955 (PARI) my(x='x+O('x^22)); Vec(serlaplace((1-sqrt(1-24*x))/12)) \\ _Michel Marcus_, Mar 04 2015
%o A221955 (Sage) [6^(n-1)*factorial(n)*catalan_number(n-1) for n in (1..30)] # _G. C. Greubel_, Apr 02 2021
%Y A221955 Sequences of the form m^(n-1)*n!*Catalan(n-1): A001813 (m=1), A052714 (or A144828) (m=2), A221954 (m=3), A052734 (m=4), A221953 (m=5), this sequence (m=6).
%Y A221955 Cf. A000108.
%K A221955 nonn
%O A221955 1,2
%A A221955 _N. J. A. Sloane_, Feb 03 2013