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A362760
Number of nonisomorphic unordered pairs of derangements of an n-set.
3
1, 0, 1, 2, 7, 16, 84, 403, 3028, 25431, 250377, 2726361, 32622807, 423310642, 5921052187, 88759485250, 1419511438134, 24123164524402, 434094104795638, 8245872981392311, 164885609163058430, 3462034812141768953, 76154237902292661820, 1751339843001023621169
OFFSET
0,4
COMMENTS
Isomorphism is up to permutation of the elements of the n-set.
LINKS
EXAMPLE
The a(3)=2 nonisomorphic pairs of derangements with permutations shown in cycle notation are:
{(123), (123)},
{(123), (132)}.
The a(4)=7 nonisomorphic pairs of derangements are:
{(12)(34), (12)(34)},
{(12)(34), (13)(24)},
{(12)(34), (1234)},
{(12)(34), (1324)},
{(1234), (1234)},
{(1234), (1243)},
{(1234), (1432)}.
CROSSREFS
Column k=2 of A362759.
Cf. A000166 (derangements), A362645.
Sequence in context: A073998 A129444 A079815 * A325510 A347601 A375880
KEYWORD
nonn
AUTHOR
Andrew Howroyd, May 02 2023
STATUS
approved