cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

Showing 1-2 of 2 results.

A101370 Number of zero-one matrices with n ones and no zero rows or columns.

Original entry on oeis.org

1, 4, 24, 196, 2016, 24976, 361792, 5997872, 111969552, 2324081728, 53089540992, 1323476327488, 35752797376128, 1040367629940352, 32441861122796672, 1079239231677587264, 38151510015777089280, 1428149538870997774080, 56435732691153773665280
Offset: 1

Views

Author

Peter J. Cameron, Jan 14 2005

Keywords

Comments

a(n) = (1/(4*n!)) * Sum_{r, s>=0} (r*s)_n / 2^(r+s), where (m)_n is the falling factorial m * (m-1) * ... * (m-n+1). [Maia and Mendez]

Examples

			a(2)=4:
[1 1] [1] [1 0] [0 1]
..... [1] [0 1] [1 0]
From _Gus Wiseman_, Nov 14 2018: (Start)
The a(3) = 24 matrices:
  [111]
.
  [11][11][110][101][10][100][011][01][010][001]
  [10][01][001][010][11][011][100][11][101][110]
.
  [1][10][10][10][100][100][01][01][010][01][010][001][001]
  [1][10][01][01][010][001][10][10][100][01][001][100][010]
  [1][01][10][01][001][010][10][01][001][10][100][010][100]
(End)
		

References

  • Georg Cantor, Gesammelte Abhandlungen mathematischen und philosophischen Inhalts, p. 435 (IV, 4. Mitteilungen zur Lehre vom Transfiniten, VIII Nr. 13), Springer, Berlin. [Rainer Rosenthal, Apr 10 2007]

Crossrefs

Cf. A000670 (the sequence P(n)), A049311 (row and column permutations allowed), A120733, A122725, A135589, A283877, A321446, A321587.

Programs

  • GAP
    P:=function(n) return Sum([1..n],x->Stirling2(n,x)*Factorial(x)); end;
    
  • GAP
    F:=function(n) return Sum([1..n],x->(-1)^(n-x)*Stirling1(n,x)*P(x)^2)/Factorial(n); end;
    
  • Mathematica
    m = 17; a670[n_] = Sum[ StirlingS2[n, k]*k!, {k, 0, n}]; Rest[ CoefficientList[ Series[ Sum[ a670[n]^2*(Log[1 + x]^n/n!), {n, 0, m}], {x, 0, m}], x]] (* Jean-François Alcover, Sep 02 2011, after g.f.  *)
    Table[Length[Select[Subsets[Tuples[Range[n],2],{n}],And[Union[First/@#]==Range[Max@@First/@#],Union[Last/@#]==Range[Max@@Last/@#]]&]],{n,5}] (* Gus Wiseman, Nov 14 2018 *)
  • PARI
    {A000670(n)=sum(k=0,n,stirling(n, k,2)*k!)}
    {a(n)=polcoeff(sum(m=0,n,A000670(m)^2*log(1+x+x*O(x^n))^m/m!),n)}
    /* Paul D. Hanna, Nov 07 2009 */

Formula

a(n) = (Sum s(n, k) * P(k)^2)/n!, where P(n) is the number of labeled total preorders on {1, ..., n} (A000670), s are signed Stirling numbers of the first kind.
G.f.: Sum_{m>=0,n>=0} Sum_{j=0..n} (-1)^(n-j)*binomial(n,j)*((1+x)^j-1)^m. - Vladeta Jovovic, Mar 25 2006
Inverse binomial transform of A007322. - Vladeta Jovovic, Aug 17 2006
G.f.: Sum_{n>=0} 1/(2-(1+x)^n)/2^(n+1). - Vladeta Jovovic, Sep 23 2006
G.f.: Sum_{n>=0} A000670(n)^2*log(1+x)^n/n! where 1/(1-x) = Sum_{n>=0} A000670(n)*log(1+x)^n/n!. - Paul D. Hanna, Nov 07 2009
a(n) ~ n! / (2^(2+log(2)/2) * (log(2))^(2*(n+1))). - Vaclav Kotesovec, Dec 31 2013

A217391 Partial sums of the squares of the ordered Bell numbers (number of preferential arrangements) A000670.

Original entry on oeis.org

1, 2, 11, 180, 5805, 298486, 22228975, 2258856824, 300194704049, 50529463186170, 10505093602625139, 2643441560563225468, 791779611505017309493, 278371498870260182630654, 113516551713466910954246903, 53143864598655784249290736512, 28309328562668956145157858372537
Offset: 0

Views

Author

Emanuele Munarini, Oct 02 2012

Keywords

Crossrefs

Partial sums of A122725.

Programs

  • Magma
    A000670:=func;
    [&+[A000670(k)^2: k in [0..n]]: n in [0..14]]; // Bruno Berselli, Oct 03 2012
    
  • Mathematica
    t[n_] := Sum[StirlingS2[n, k]k!, {k, 0, n}]; Table[Sum[t[k]^2, {k, 0, n}], {n, 0, 100}]
  • Maxima
    t(n):=sum(stirling2(n,k)*k!,k,0,n);
    makelist(sum(t(k)^2,k,0,n),n,0,40);
    
  • PARI
    for(n=0,30, print1(sum(k=0,n, (sum(j=0,k, j!*stirling(k,j,2)))^2), ", ")) \\ G. C. Greubel, Feb 07 2018

Formula

a(n) = Sum_{k=0..n} t(k)^2 where t = A000670 (ordered Bell numbers).
a(n) ~ (n!)^2 / (4 * (log(2))^(2*n+2)). - Vaclav Kotesovec, Nov 08 2014
Showing 1-2 of 2 results.