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A226466 The number of endomorphisms of the symmetric inverse monoid on the set {1..n} 1
1, 3, 14, 54, 306, 918, 4524, 25560, 168828, 1315764, 11998584, 125358192, 1466062200, 18835528104, 262376016912, 3927709053792, 62795044663056, 1067217284481840, 19208039592749472, 364940846656681536, 7298740111856220576, 153273039685710932448, 3372003538678423189440 (list; graph; refs; listen; history; text; internal format)
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: A166680 A104191 A151540 * A026544 A026527 A037786

Adjacent sequences:  A226463 A226464 A226465 * A226467 A226468 A226469

KEYWORD

nonn

AUTHOR

James Mitchell, Jun 08 2013

STATUS

approved

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Last modified December 12 15:01 EST 2017. Contains 295939 sequences.