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A000240 Rencontres numbers: number of permutations of [n] with exactly one fixed point.
(Formerly M2763 N1111)
27
1, 0, 3, 8, 45, 264, 1855, 14832, 133497, 1334960, 14684571, 176214840, 2290792933, 32071101048, 481066515735, 7697064251744, 130850092279665, 2355301661033952, 44750731559645107, 895014631192902120, 18795307255050944541, 413496759611120779880 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

a(n) is also the number of permutations of [n] having no circular succession. A circular succession in a permutation p of [n] is either a pair p(i), p(i+1), where p(i+1)=p(i)+1 or the pair p(n), p(1) if p(1)=p(n)+1. a(4)=8 because we have 1324, 1432, 4132, 2143, 2413, 3214, 3241, and 4321. - Emeric Deutsch, Sep 06 2010

REFERENCES

J. Riordan, An Introduction to Combinatorial Analysis, Wiley, 1958, p. 65.

N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

LINKS

T. D. Noe, Table of n, a(n) for n=1..100

S. K. Das and N. Deo, Rencontres graphs: a family of bipartite graphs, Fib. Quart., Vol. 25, No. 3, August 1987, 250-262.

FindStat - Combinatorial Statistic Finder, The number of fixed points of a permutation

I. Kaplansky, Symbolic solution of certain problems in permutations, Bull. Amer. Math. Soc., 50 (1944), 906-914.

S. M. Tanny, Permutations and successions, J. Combinatorial Theory, Series A, 21 (1976), 196-202.

FORMULA

E.g.f.: x*exp(-x)/(1-x). [corrected by Vaclav Kotesovec, Sep 26 2012]

a(n) = sum((-1)^k*n!/k!, k=0..n-1).

a(n) = A180188(n,0). - Emeric Deutsch, Sep 06 2010

E.g.f.: x*A(x) where A(x) is the e.g.f. for A000166. - Geoffrey Critzer, Jan 14 2012

a(n) = n*a(n-1)-(-1)^n*n = A000166(n)-(-1)^n = n*A000166(n-1) = A000387(n+1)*2/(n+1) = A000449(n+2)*6/((n+1)*(n+2)).

a(n) = n*floor(((n-1)!+1)/e), n>1. - Gary Detlefs, Jul 13 2010

lim_{n->infinity} n!/a(n) = e = 2.71828...

EXAMPLE

a(3) = 3 because the permutations of (1,2,3) with one fixed point are (1,2), (1,3), (2,3).

MAPLE

G(x):=exp(-x)/(1-x)*x: f[0]:=G(x): for n from 1 to 26 do f[n]:=diff(f[n-1], x) od: x:=0: seq(f[n], n=1..22); # Zerinvary Lajos, Apr 03 2009

A000240 := proc(n)

        n!*add((-1)^k/k!, k=0..n-1) ;

end proc: # R. J. Mathar, Jul 09 2012

MATHEMATICA

Table[Subfactorial[n]-(-1)^n, {n, 1, 25}] (* Zerinvary Lajos, Jul 10 2009, updated for offset 1 by Jean-Fran├žois Alcover, Jan 10 2014 *)

Table[n!*Sum[(-1)^k/k!, {k, 0, n-1}], {n, 1, 25}] (* Vaclav Kotesovec, Sep 26 2012 *)

Table[n!*SeriesCoefficient[x*E^(-x)/(1-x), {x, 0, n}], {n, 1, 25}] (* Vaclav Kotesovec, Sep 26 2012 *)

PROG

(Python)

a=0

for i in range(1, 51):

. a = (a-(-1)**i)*i

. print a,          # Alex Ratushnyak, Apr 20 2012

(PARI) x='x+O('x^66); Vec( serlaplace(x*exp(-x)/(1-x)) ) \\ Joerg Arndt, Feb 19 2014

CROSSREFS

Cf. A008290, A000166, A000387, A000449, A000475, A129135, etc.

A diagonal of A008291.

Cf. A180188, A170942.

Sequence in context: A074435 A039647 A071533 * A182390 A132103 A180508

Adjacent sequences:  A000237 A000238 A000239 * A000241 A000242 A000243

KEYWORD

nonn,easy,nice

AUTHOR

N. J. A. Sloane, Simon Plouffe

STATUS

approved

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Last modified December 20 20:33 EST 2014. Contains 252289 sequences.