A038094 Number of rooted graphs on n labeled nodes where the root has degree 2.

6, 96, 1920, 61440, 3440640, 352321536, 67645734912, 24739011624960, 17416264183971840, 23779006032516218880, 63309225660971181146112, 330036748754793764694786048, 3379576307249088150474609131520

Offset

3,1

Links

Vincenzo Librandi, Table of n, a(n) for n = 3..80

Formula

a(n) = n * binomial(n-1, 2) * 2^binomial(n-1, 2).

a(n) = n * A103904(n-1) for n >= 3. - Andrew Howroyd, Nov 23 2020

Mathematica

Table[n*Binomial[n-1, 2]*2^Binomial[n-1, 2], {n, 3, 20}] (* Vaclav Kotesovec, Mar 29 2014 *)

Prog

(Magma) [n*Binomial(n-1, 2)*2^Binomial(n-1, 2): n in [3..20]]; // Vincenzo Librandi, Mar 29 2014
(PARI) a(n) = {n * binomial(n-1, 2) * 2^binomial(n-1, 2)} \\ Andrew Howroyd, Nov 23 2020

Crossrefs

Cf. A006125, A038095, A038096, A038097, A103904.

Sequence in context: A139743 A361737 A156460 * A346184 A304646 A251576

Adjacent sequences: A038091 A038092 A038093 * A038095 A038096 A038097

Keyword

nonn,easy

Author

Christian G. Bower, Jan 04 1999

Status

approved