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A038094 Number of rooted graphs on n labeled nodes where the root has degree 2. 6
6, 96, 1920, 61440, 3440640, 352321536, 67645734912, 24739011624960, 17416264183971840, 23779006032516218880, 63309225660971181146112, 330036748754793764694786048, 3379576307249088150474609131520 (list; graph; refs; listen; history; text; internal format)
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: A001805 A139743 A156460 * A304646 A251576 A126151

Adjacent sequences:  A038091 A038092 A038093 * A038095 A038096 A038097

KEYWORD

nonn,easy

AUTHOR

Christian G. Bower, Jan 04 1999

STATUS

approved

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Last modified January 17 16:45 EST 2021. Contains 340247 sequences. (Running on oeis4.)