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A007837 Number of partitions of n-set with distinct block sizes. 72
1, 1, 1, 4, 5, 16, 82, 169, 541, 2272, 17966, 44419, 201830, 802751, 4897453, 52275409, 166257661, 840363296, 4321172134, 24358246735, 183351656650, 2762567051857, 10112898715063, 62269802986835, 343651382271526, 2352104168848091, 15649414071734847 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

LINKS

Alois P. Heinz, Table of n, a(n) for n = 0..700

Philippe Flajolet, Éric Fusy, Xavier Gourdon, Daniel Panario and Nicolas Pouyanne, A Hybrid of Darboux's Method and Singularity Analysis in Combinatorial Asymptotics, Fig. 3, arXiv:math/0606370 [math.CO], 2006.

Knopfmacher, A., Odlyzko, A. M., Pittel, B., Richmond, L. B., Stark, D., Szekeres, G. and Wormald, N. C., The asymptotic number of set partitions with unequal block sizes, Electron. J. Combin., 6 (1999), no. 1, Research Paper 2, 36 pp.

Gus Wiseman, Sequences counting and ranking multiset partitions whose part lengths, sums, or averages are constant or strict.

FORMULA

E.g.f.: Product_{m >= 1} (1+x^m/m!).

a(n) = Sum_{k=1..n} (n-1)!/(n-k)!*b(k)*a(n-k), where b(k) = Sum_{d divides k} (-d)*(-d!)^(-k/d) and a(0) = 1. - Vladeta Jovovic, Oct 13 2002

E.g.f.: exp(Sum_{k>=1} Sum_{j>=1} (-1)^(k+1)*x^(j*k)/(k*(j!)^k)). - Ilya Gutkovskiy, Jun 18 2018

EXAMPLE

From Gus Wiseman, Jul 13 2019: (Start)

The a(1) = 1 through a(5) = 16 set partitions with distinct block sizes:

  {{1}}  {{1,2}}  {{1,2,3}}    {{1,2,3,4}}    {{1,2,3,4,5}}

                  {{1},{2,3}}  {{1},{2,3,4}}  {{1},{2,3,4,5}}

                  {{1,2},{3}}  {{1,2,3},{4}}  {{1,2},{3,4,5}}

                  {{1,3},{2}}  {{1,2,4},{3}}  {{1,2,3},{4,5}}

                               {{1,3,4},{2}}  {{1,2,3,4},{5}}

                                              {{1,2,3,5},{4}}

                                              {{1,2,4},{3,5}}

                                              {{1,2,4,5},{3}}

                                              {{1,2,5},{3,4}}

                                              {{1,3},{2,4,5}}

                                              {{1,3,4},{2,5}}

                                              {{1,3,4,5},{2}}

                                              {{1,3,5},{2,4}}

                                              {{1,4},{2,3,5}}

                                              {{1,4,5},{2,3}}

                                              {{1,5},{2,3,4}}

(End)

MAPLE

a:= proc(n) option remember; `if`(n=0, 1, add(add((-d)*(-d!)^(-k/d),

       d=numtheory[divisors](k))*(n-1)!/(n-k)!*a(n-k), k=1..n))

    end:

seq(a(n), n=0..30);  # Alois P. Heinz, Sep 06 2008

# second Maple program:

A007837 := proc(n) option remember; local k; `if`(n = 0, 1,

add(binomial(n-1, k-1) * A182927(k) * A007837(n-k), k = 1..n)) end:

seq(A007837(i), i=0..24); # Peter Luschny, Apr 25 2011

MATHEMATICA

nn=20; p=Product[1+x^i/i!, {i, 1, nn}]; Drop[Range[0, nn]!CoefficientList[ Series[p, {x, 0, nn}], x], 1]  (* Geoffrey Critzer, Sep 22 2012 *)

a[0]=1; a[n_] := a[n] = Sum[(n-1)!/(n-k)!*DivisorSum[k, -#*(-#!)^(-k/#)&]* a[n-k], {k, 1, n}]; Table[a[n], {n, 0, 30}] (* Jean-François Alcover, Nov 23 2015, after Vladeta Jovovic *)

PROG

(PARI) {my(n=20); Vec(serlaplace(prod(k=1, n, (1+x^k/k!) + O(x*x^n))))} \\ Andrew Howroyd, Dec 21 2017

CROSSREFS

Row sums of A131632 or A262072 or A262078 or A309992.

Cf. A000110, A005651, A007838, A032011, A035470, A038041, A178682, A265950, A271423, A275780, A326026, A326514, A326517, A326533.

Column k=0 of A327869.

Sequence in context: A110278 A013628 A127007 * A032219 A032144 A032049

Adjacent sequences:  A007834 A007835 A007836 * A007838 A007839 A007840

KEYWORD

nonn

AUTHOR

Arnold Knopfmacher

EXTENSIONS

More terms from Christian G. Bower

a(0)=1 prepended by Alois P. Heinz, Aug 29 2015

STATUS

approved

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Last modified February 27 20:32 EST 2021. Contains 341658 sequences. (Running on oeis4.)