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A094577 Central Peirce numbers. Number of set partitions of {1,2,..,2n+1} in which n+1 is the smallest of its block. 6
1, 3, 27, 409, 9089, 272947, 10515147, 501178937, 28773452321, 1949230218691, 153281759047387, 13806215066685433, 1408621900803060705, 161278353358629226675, 20555596673435403499083, 2896227959507289559616217, 448371253145121338801335489 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Let P(n,k) be the number of set partitions of {1,2,..,n} in which k is the smallest of its block. These numbers were introduced by C. S. Peirce (see reference, page 48). If this triangle is displayed as in A123346 (or A011971) then a(n) = A011971(2n, n) are the central Pierce numbers. - Peter Luschny, Jan 18 2011

REFERENCES

D. E. Knuth, TAOCP, Vol. 4, Section 7.2.1.5.

LINKS

Alois P. Heinz, Table of n, a(n) for n = 0..150

C. S. Peirce, On the Algebra of Logic, American Journal of Mathematics 3, (1880), 15 - 57.

FORMULA

Sum_{k=0..n} binomial(n,k)*Bell(2*n-k). - Vladeta Jovovic

Or, Sum_{k=0..n} (-1)^k*binomial(n, k)*Bell(2*n-k+1).

a(n) = exp(-1)*Sum_{k>=0} (k(k+1))^n/k!. - Benoit Cloitre, Dec 30 2005

EXAMPLE

n = 1, S = {1, 2, 3}. k = n+1 = 2. Thus a(1) = card { 13|2, 1|23, 1|2|3 } = 3. - Peter Luschny, Jan 18 2011

MAPLE

seq(add(binomial(n, k)*(bell(n+k)), k=0..n), n=0..14); # Zerinvary Lajos, Dec 01 2006

# The objective of this implementation is efficiency.

# m -> [a(0), a(1), ..., a(m-1)] for m > 0.

A094577_list := proc(m)

   local A, R, M, n, k, j;

   M := m+m-1; A := array(1..M);

   j := 1; R := 1; A[1] := 1;

   for n from 2 to M do

      A[n] := A[1];

      for k from n by -1 to 2 do

         A[k-1] := A[k-1] + A[k]

      od;

      if is(n, odd) then

         j := j+1; R := R, A[j] fi

   od;

[R] end:

A094577_list(100); # example call - Peter Luschny, Jan 17 2011

MATHEMATICA

f[n_] := Sum[Binomial[n, k]*BellB[2 n - k], {k, 0, n}]; Array[f, 15, 0]

PROG

(Python)

# requires python 3.2 or higher. Otherwise use def'n of accumulate in python docs.

from itertools import accumulate

A094577_list, blist, b = [1], [1], 1

for n in range(2, 502):

....blist = list(accumulate([b]+blist))

....b = blist[-1]

....blist = list(accumulate([b]+blist))

....b = blist[-1]

....A094577_list.append(blist[-n])

# Chai Wah Wu, Sep 02 2014, updated Chai Wah Wu, Sep 20 2014

CROSSREFS

Cf. A094574, A020556.

Main diagonal of array in A011971.

Sequence in context: A141057 A201696 A011781 * A221624 A108525 A136719

Adjacent sequences:  A094574 A094575 A094576 * A094578 A094579 A094580

KEYWORD

nonn

AUTHOR

Vladeta Jovovic, May 12 2004

STATUS

approved

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Last modified November 13 11:24 EST 2018. Contains 317133 sequences. (Running on oeis4.)