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 A132431 For n>0, let B_n be the subsemigroup of the full transformation monoid on the n-set [n] generated by the following functions: Let x be a certain element in [n]. Now the generators of B are those functions which map either x to any distinct element y in [n] leaving all the other elements fixed, or y to x leaving all the other elements fixed. Then a(n) = number of elements in B_n. 1
 0, 2, 9, 88, 1385, 24336, 466753, 9906688, 233522577, 6093136000, 174912502721, 5487091383456, 186891076515481, 6870622015481056, 271195480556337345, 11440127985767481856, 513639921634424850977, 24455974520989478444544, 1230835712617872016215265 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Let b(n)=n^n be the cardinality of the full transformation monoid. The sequence of quotients a(n)/b(n) converges to 1-1/e. a(n) = A060226(n) - A062119(n) + A002378(n-1). - Reinhard Zumkeller, Aug 27 2012 REFERENCES S. Bogner, Eine Praesentation der Halbgruppe der singularen zyklisch-monotonen Abbildungen UND eine von Idempotenten erzeugte Unterhalbgruppe von T_n (Studienarbeit in Informatik, Advisor: Klaus Leeb), Friedrich-Alexander-Universitaet Erlangen-Nuernberg, 2007. LINKS Reinhard Zumkeller, Table of n, a(n) for n = 1..250 FORMULA a(n) = n^n - n(n-1)^(n-1) - (n-1)n! + n(n-1). a(n) = n*(n-1) + sum_{k=1..n-2} k*Stirling2(n-1,k)*k!*C(n,k). MATHEMATICA Join[{0}, Table[n^n-n (n-1)^(n-1)-(n-1)n!+n(n-1), {n, 2, 20}]] (* Harvey P. Dale, Jun 07 2018 *) PROG (Haskell) a132431 n = a060226 n - a062119 n + a002378 (n - 1) -- Reinhard Zumkeller, Aug 27 2012 CROSSREFS Cf. A000312, A060226. Sequence in context: A135747 A270862 A259794 * A228509 A001192 A006120 Adjacent sequences:  A132428 A132429 A132430 * A132432 A132433 A132434 KEYWORD nice,nonn AUTHOR Simon Bogner (sisibogn(AT)stud.informatik.uni-erlangen.de), Nov 20 2007 STATUS approved

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Last modified July 29 15:44 EDT 2021. Contains 346346 sequences. (Running on oeis4.)