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

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A052889 Number of rooted set partitions. 13
0, 1, 2, 6, 20, 75, 312, 1421, 7016, 37260, 211470, 1275725, 8142840, 54776761, 387022118, 2863489830, 22127336720, 178162416499, 1491567656472, 12959459317021, 116654844101140, 1086207322942812, 10447135955448522, 103654461984288429, 1059648140522024304 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,3
COMMENTS
Total number of blocks of size one in all set partitions of set {1..n}. - Wouter Meeussen, Jul 28 2003
With offset 1, number of permutations beginning with 12 and avoiding 12-3.
a(n) = number of partitions of {1...n+1} containing exactly one pair of consecutive integers, counted within a block. With offset t-1, number of partitions of {1...N} containing one string of t consecutive integers, where N=n+j, t=2+j, j = 0,1,2,.... - Augustine O. Munagi, Apr 10 2005
LINKS
Adam M. Goyt and Lara K. Pudwell, Avoiding colored partitions of two elements in the pattern sense, arXiv preprint arXiv:1203.3786 [math.CO], 2012. - From N. J. A. Sloane, Sep 17 2012
Jia Huang and Erkko Lehtonen, Associative-commutative spectra for some varieties of groupoids, arXiv:2401.15786 [math.CO], 2024. See p. 13.
Sergey Kitaev, Generalized pattern avoidance with additional restrictions, Sem. Lothar. Combinat. B48e (2003); arXiv:math/0205215 [math.CO].
Sergey Kitaev and Toufik Mansour, Simultaneous avoidance of generalized patterns, arXiv:math/0205182 [math.CO], 2002.
Augustine O. Munagi, Set Partitions with Successions and Separations, IJMMS 2005:3 (2005),451-463.
FORMULA
E.g.f.: exp(exp(x)-1)*x.
a(n) = n*Bell(n-1). - Vladeta Jovovic, Sep 14 2003
Let A be the upper Hessenberg matrix of order n defined by: A[i,i-1]=-1, A[i,j]=binomial(j-1,i-1), (i<=j), and A[i,j]=0 otherwise. Then, for n>=1, a(n)=(-1)^(n-1)*coeff(charpoly(A,x),x). - Milan Janjic, Jul 08 2010
EXAMPLE
a(3) = 6 because the partitions of {1, 2, 3, 4} containing a pair of consecutive integers are 124/3, 134/2, 14/23, 12/3/4, 1/23/4, 1/2/34.
MAPLE
spec := [S, {B=Set(C), C=Set(Z, 1 <= card), S=Prod(Z, B)}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);
Explanation of above combstruct commands using generating functions, from Mitch Harris, Jul 28 2003:
Z = an atom (each atom used is labeled), gf: Z(x) = x
C = Set(Z, card <= 1) is the set of positive integers; gf: C(x) = e^(Z(x)) - 1 = e^x - 1 (the -1 removes the empty set); [x^n]C = 1 means there is exactly one set with n atoms since each atom is labeled
B = Set(C) the set of (ordered) sets of integers = ordered set partitions; gf: B(x) = e^C(x) = e^(e^x - 1)
S = Prod(Z, B) pairs of an atom (Z) and an ordered set partition = an ordered set partition with an adjoining single atom. The adjoining atom corresponds to choosing a "root" in the partition; gf: S(x) = x B(x) = x*e^(e^x-1)
A052889 := n -> `if`(n=0, 0, n*combinat[bell](n-1)):
seq(A052889(n), n=0..20); # Peter Luschny, Apr 19 2011
MATHEMATICA
a=Exp[x]-1; Range[0, 20]! CoefficientList[Series[ x Exp[a], {x, 0, 20}], x] (* Geoffrey Critzer, Nov 25 2011 *)
CROSSREFS
Second column of triangle A033306.
Cf. A000110.
Column k=1 of A175757.
Sequence in context: A150168 A145870 A134957 * A263901 A150169 A083691
KEYWORD
easy,nonn
AUTHOR
encyclopedia(AT)pommard.inria.fr, Jan 25 2000
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.

License Agreements, Terms of Use, Privacy Policy. .

Last modified February 26 12:26 EST 2024. Contains 370352 sequences. (Running on oeis4.)