The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A144086 Number of partial bijections (or subpermutations) of an n-element set with exactly 1 fixed point. 3
 0, 1, 2, 12, 72, 540, 4680, 46200, 510720, 6244560, 83613600, 1216131840, 19084222080, 321271030080, 5773503415680, 110288062684800, 2231100039168000, 47640952315756800, 1070630750168179200, 25255541547460224000, 623884298434645248000, 16104652019138319436800 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS Vincenzo Librandi, Table of n, a(n) for n = 0..200 A. Laradji and A. Umar, Combinatorial results for the symmetric inverse semigroup, Semigroup Forum 75, (2007), 221-236. FORMULA a(n) = A144088(n, 1) and a(n) = n*A144085(n-1). E.g.f.: (x^k/k!)*exp(x^2/(1-x))/(1-x) where k=1. - Joerg Arndt, Jul 11 2011 a(n) = n!*Sum_{m=0..n-1} (-1^m/m!)*Sum_{j=0..n-m} C(n-m)/j!; (n-1)*a(n) = n*(2*n-3)*a(n-1) - n*(n-1)*(n-4)*a(n-2) - n*(n-1)*(n-2)*a(n-3), a(1)=1 and a(n)=0 if n < 1. a(n) ~ n^(n+1/4) * exp(2*sqrt(n)-n-3/2) / sqrt(2) * (1 + 31/(48*sqrt(n))). - Vaclav Kotesovec, Feb 24 2014 EXAMPLE a(3) = 12 because there are exactly 12 partial bijections (on a 3-element set) with exactly 1 fixed point, namely: (1)->(1), (2)->(2), (3)->(3), (1,2)->(1,3), (1,2)->(3,2), (1,3)->(1,2), (1,3)->(2,3), (2,3)->(2,1), (2,3)->(1,3), (1,2,3)->(1,3,2), (1,2,3)->(3,2,1), (1,2,3)->(2,1,3) - the mappings are coordinate-wise. MATHEMATICA CoefficientList[Series[x*E^(x^2/(1-x))/(1-x), {x, 0, 20}], x] * Range[0, 20]! (* Vaclav Kotesovec, Feb 24 2014 *) PROG (PARI) x='x+O('x^66); /* that many terms */ k=1; egf=x^k/k!*exp(x^2/(1-x))/(1-x); Vec(serlaplace(egf)) /* show terms, starting with 1 */ /* Joerg Arndt, Jul 11 2011 */ CROSSREFS Cf. A144088, A144085. Sequence in context: A052833 A277490 A296975 * A348767 A335786 A005443 Adjacent sequences:  A144083 A144084 A144085 * A144087 A144088 A144089 KEYWORD nonn AUTHOR Abdullahi Umar, Sep 10 2008, Sep 15 2008 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified May 28 15:04 EDT 2022. Contains 354115 sequences. (Running on oeis4.)