A362900 Number of nonisomorphic unordered pairs of fixed-point-free endofunctions on an n-set.

1, 0, 1, 9, 162, 4527, 172335, 7861940, 416446379, 25076668511, 1692214417496, 126525497074469, 10384653020019554, 928348695659951013, 89797089935616345473, 9344984104905250973209, 1041167026926648579218267, 123655975822561996200923033, 15595901625395079379351443550

Offset

0,4

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

In the following example the notation 211 corresponds to the fixed-point-free mapping {1->2, 2->1, 3->1}.
The a(3) = 9 nonisomorphic pairs of endofunctions are: {211, 211}, {211, 212}, {211, 231}, {211, 232}, {211, 311}, {211, 312}, {211, 332}, {231, 231}, {231, 312}.

Crossrefs

Column k=2 of A362899.

Cf. A054745 (allowing fixed-points).

Sequence in context: A237024 A156273 A051232 * A157574 A077280 A297436

Adjacent sequences: A362897 A362898 A362899 * A362901 A362902 A362903

Keyword

nonn

Author

Andrew Howroyd, May 10 2023

Status

approved