

A272582


The number of strongly connected digraphs with n vertices and n+1 edges.


1



0, 9, 84, 720, 6480, 63000, 665280, 7620480, 94348800, 1257379200, 17962560000, 273988915200, 4446092851200, 76498950528000, 1391365527552000, 26676557107200000, 537799391281152000, 11373816888225792000, 251805357846282240000, 5824367407574876160000
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OFFSET

2,2


COMMENTS

Wright also gives the number of strongly connected digraphs with n vertices and n+2 edges, 0, 6, 316, 6440, 107850, 1719060, 27476400, ... (offset 2) in terms of a polynomial of order 5 multiplied by n!.  R. J. Mathar, May 12 2016


LINKS



FORMULA

a(n) = (n2)*(n+3)*n!/4.
Dfinite with recurrence (n+1)*(n4)*a(n) +(n1)*(n3)*(n+2)*a(n1)=0.  R. J. Mathar, Mar 11 2021


MATHEMATICA



PROG

(Python)
from __future__ import print_function
from sympy import factorial
for n in range(2, 500):
print((int)((n2)*(n+3)*factorial(n)/4), end=", ")


CROSSREFS



KEYWORD

nonn,easy


AUTHOR



STATUS

approved



