OFFSET
1,3
COMMENTS
There is a rather difficult formula (simplified in 1973). The subsequent published value 6222928 for n=6 needs to be verified.
The correct value is 6222400. Terms up to a(7) have been confirmed by brute force using digraphs generated by nauty. - Andrew Howroyd, Jan 12 2022
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..50
V. A. Liskovets, The number of strongly connected directed graphs, Mat. Notes, 8 (1970), 877-882
PROG
(PARI) \\ See PARI link in A350794 for program code.
A049387seq(15) \\ Andrew Howroyd, Jan 22 2022
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
Terms a(6) and beyond from Andrew Howroyd, Jan 12 2022
STATUS
approved