A226466 The number of endomorphisms of the symmetric inverse monoid on the set {1..n}.

1, 3, 14, 54, 306, 918, 4524, 25560, 168828, 1315764, 11998584, 125358192, 1466062200, 18835528104, 262376016912, 3927709053792, 62795044663056, 1067217284481840, 19208039592749472, 364940846656681536, 7298740111856220576, 153273039685710932448, 3372003538678423189440

Offset

0,2

Links

James Mitchell, Table of n, a(n) for n = 0..100

B. M. Schein and B. Teclezghi, Endomorphisms of finite symmetric inverse semigroups, J. Algebra, 198 (1997) 300-310.

Prog

(PARI) a(n)=if(n==0, return (1), if(n<5, return([3, 14, 54, 306][n]))); n!*(3+sum(m=0, n, sum(k=0, m\2, 2^(m-3*k)/((n-m)!*(m-2*k)!*k!))))

Crossrefs

Cf. A226223.

Sequence in context: A104191 A318125 A151540 * A363964 A322938 A026544

Adjacent sequences: A226463 A226464 A226465 * A226467 A226468 A226469

Keyword

nonn

Author

James Mitchell, Jun 08 2013

Status

approved