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 A317527 #20 Feb 16 2025 08:33:56
%S A317527 0,0,3,24,180,1440,12600,120960,1270080,14515200,179625600,2395008000,
%T A317527 34248614400,523069747200,8499883392000,146459529216000,
%U A317527 2667655710720000,51218989645824000,1033983353475072000,21896118073589760000,485363950631239680000,11240007277776076800000
%N A317527 Number of edges in the n-alternating group graph.
%C A317527 Looks like the denominators of g.f.: (1-x)*exp(-x) + x^2*(Chi(x) - Shi(x)), for cosh and sinh integral functions. - _Benedict W. J. Irwin_, Jun 04 2018
%H A317527 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/AlternatingGroupGraph.html">Alternating Group Graph</a>
%H A317527 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/EdgeCount.html">Edge Count</a>
%F A317527 a(n) = n!*(n - 2)/2 for n > 1.
%F A317527 a(n) = 3 * A005990(n-1) for n>1. - _Alois P. Heinz_, Jul 30 2018
%F A317527 E.g.f.: x^3/(2*(x - 1)^2).
%t A317527 Join[{0}, Table[n! (n - 2)/2, {n, 2, 20}]]
%t A317527 CoefficientList[Series[x^2/(2 (-1 + x)^2), {x, 0, 19}], x] Range[20]!
%o A317527 (Magma) [0] cat [Factorial(n)*(n-2)/2: n in [2..25]]; // _Vincenzo Librandi_, Jul 31 2018
%Y A317527 Cf. A005990, A181967.
%K A317527 nonn
%O A317527 1,3
%A A317527 _Eric W. Weisstein_, Jul 30 2018