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

1,3

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

Table of n, a(n) for n=1..22.

Eric Weisstein's World of Mathematics, Alternating Group Graph

Eric Weisstein's World of Mathematics, Edge Count

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).

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]!

Prog

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

Crossrefs

Cf. A005990, A181967.

Sequence in context: A292293 A073985 A197209 * A181967 A144087 A110347

Adjacent sequences: A317524 A317525 A317526 * A317528 A317529 A317530

Keyword

nonn

Author

Eric W. Weisstein, Jul 30 2018

Status

approved