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%I #17 Jan 22 2020 14:40:14
%S 1,3,14,54,306,918,4524,25560,168828,1315764,11998584,125358192,
%T 1466062200,18835528104,262376016912,3927709053792,62795044663056,
%U 1067217284481840,19208039592749472,364940846656681536,7298740111856220576,153273039685710932448,3372003538678423189440
%N The number of endomorphisms of the symmetric inverse monoid on the set {1..n}.
%H James Mitchell, <a href="/A226466/b226466.txt">Table of n, a(n) for n = 0..100</a>
%H B. M. Schein and B. Teclezghi, <a href="https://doi.org/10.1006/jabr.1997.7132">Endomorphisms of finite symmetric inverse semigroups</a>, J. Algebra, 198 (1997) 300-310.
%o (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!))))
%Y Cf. A226223.
%K nonn
%O 0,2
%A _James Mitchell_, Jun 08 2013