A317527 Number of edges in the n-alternating group graph.

0, 0, 3, 24, 180, 1440, 12600, 120960, 1270080, 14515200, 179625600, 2395008000, 34248614400, 523069747200, 8499883392000, 146459529216000, 2667655710720000, 51218989645824000, 1033983353475072000, 21896118073589760000, 485363950631239680000, 11240007277776076800000

Offset: 1

Author

Eric W. Weisstein, Jul 30 2018

Keywords

• nonn

Comments

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

Links

• Eric Weisstein's World of Mathematics, Alternating Group Graph
• Eric Weisstein's World of Mathematics, Edge Count

Crossrefs

Cf. A005990, A181967.

Programs

Magma

[0] cat [Factorial(n)*(n-2)/2: n in [2..25]]; // Vincenzo Librandi, Jul 31 2018

Mathematica

Join[{0}, Table[n! (n - 2)/2, {n, 2, 20}]]
CoefficientList[Series[x^2/(2 (-1 + x)^2), {x, 0, 19}], x] Range[20]!

Formula

a(n) = n!*(n - 2)/2 for n > 1.

a(n) = 3 * A005990(n-1) for n>1. - Alois P. Heinz, Jul 30 2018

E.g.f.: x^3/(2*(x - 1)^2).