OFFSET
0,3
COMMENTS
Isomorphism is up to permutation of the elements of the n-set.
LINKS
Andrew Howroyd, Table of n, a(n) for n = 0..50
EXAMPLE
The a(4)=10 pairs of involutions are:
{(), ()},
{(), (34)},
{(), (12)(34)},
{(34), (34)},
{(34), (23)},
{(34), (12)},
{(34), (12)(34)},
{(34), (13)(24)},
{(12)(34), (12)(34)},
{(12)(34), (13)(24)}.
CROSSREFS
KEYWORD
nonn
AUTHOR
Andrew Howroyd, May 01 2023
STATUS
approved