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 1-7 of 7 results.

A055165 Number of invertible n X n matrices with entries equal to 0 or 1.

Original entry on oeis.org

1, 1, 6, 174, 22560, 12514320, 28836612000, 270345669985440, 10160459763342013440
Offset: 0

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Author

Ulrich Hermisson (uhermiss(AT)server1.rz.uni-leipzig.de), Jun 18 2000

Keywords

Comments

All eigenvalues are nonzero.

Examples

			For n=2 the 6 matrices are {{{0, 1}, {1, 0}}, {{0, 1}, {1, 1}}, {{1, 0}, {0, 1}}, {{1, 0}, {1, 1}}, {{1, 1}, {0, 1}}, {{1, 1}, {1, 0}}}.
		

Crossrefs

Cf. A056990, A056989, A046747, A055165, A002416, A003024 (positive definite matrices).
A046747(n) + a(n) = 2^(n^2) = total number of n X n (0, 1) matrices = sequence A002416.
Main diagonal of A064230.

Programs

  • PARI
    a(n)=sum(t=0,2^n^2-1,!!matdet(matrix(n,n,i,j,(t>>(i*n+j-n-1))%2))) \\ Charles R Greathouse IV, Feb 09 2016
    
  • Python
    from itertools import product
    from sympy import Matrix
    def A055165(n): return sum(1 for s in product([0,1],repeat=n**2) if Matrix(n,n,s).det() != 0) # Chai Wah Wu, Sep 24 2021

Formula

For an asymptotic estimate see A046747. A002884 is a lower bound. A002416 is an upper bound.
a(n) = n! * A088389(n). - Gerald McGarvey, Oct 20 2007

Extensions

More terms from Miodrag Zivkovic (ezivkovm(AT)matf.bg.ac.rs), Feb 28 2006
Description improved by Jeffrey Shallit, Feb 17 2016
a(0)=1 prepended by Alois P. Heinz, Jun 18 2022

A000410 Number of singular n X n rational (0,1)-matrices.

Original entry on oeis.org

0, 0, 6, 425, 65625, 27894671, 35716401889, 144866174953833
Offset: 1

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Author

Keywords

Comments

Number of all n X n (0,1)-matrices having distinct, nonzero ordered rows and determinant 0 - compare A000409.
a(n) is the number of singular n X n rational {0,1}-matrices with no zero rows and with all rows distinct, up to permutation of rows and so a(n) = binomial(2^n-1,n) - A088389(n). Cf. A116506, A116507, A116527, A116532. - Vladeta Jovovic, Apr 03 2006

References

  • 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).

Crossrefs

Formula

n! * a(n) = A046747(n) - 2^(n^2) + n! * binomial(2^n -1, n).

Extensions

n=7 term from Guenter M. Ziegler (ziegler(AT)math.TU-Berlin.DE)
a(8) from Vladeta Jovovic, Mar 28 2006

A064231 Triangle read by rows: T(n,k) = number of rational (+1,-1) matrices of rank k (n >= 1, 1 <= k <= n).

Original entry on oeis.org

2, 8, 8, 32, 288, 192, 128, 6272, 36864, 22272, 512, 115200, 3456000, 18432000, 11550720, 2048, 1968128, 243302400, 6471168000, 36373708800, 25629327360, 8192, 32514048, 14809546752, 1557061632000, 43378316083200, 281770208133120
Offset: 1

Views

Author

N. J. A. Sloane, Sep 23 2001

Keywords

Comments

Rows add to 2^(n^2) = A002416. - Jonathan Vos Post, Feb 27 2011
Komlos and later Kahn, Komlos and Szemeredi show that almost all such matrices are invertible.

Examples

			2; 8,8; 32,288,192; 128,6272,36864,22272; ...
		

References

  • J. Kahn, J. Komlos and E. Szemeredi: On the probability that a random +-1 matrix is singular, J. AMS 8 (1995), 223-240.
  • J. Komlos, On the determinants of random matrices, Studia Sci. Math. Hungar., 3 (1968), 387-399.

Crossrefs

Programs

  • PARI
    T=matrix(4,4); { for(n=1,4, mm=matrix(n,n); for(k=1,n, T[n,k]=0); forvec(x=vector(n*n,i,[0,1]), for(i=1,n, for(j=1,n,mm[i,j]=(-1)^x[i+n*(j-1)])); T[n,matrank(mm)]++); for(k=1,n,print1(T[n,k], if(k
    				

Extensions

More terms and PARI code from Michael Somos, Sep 25 2001
More terms from Vladeta Jovovic, Apr 02 2006
Offset changed to 1 by T. D. Noe, Mar 02 2011

A086875 Sum of rank(M) over all n X n matrices over Z with all entries zero or one.

Original entry on oeis.org

1, 21, 1147, 211965, 143331811, 366753209781
Offset: 1

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Author

Tom Womack (tom(AT)womack.net), Aug 21 2003

Keywords

Comments

The unlikely-looking symbol "+:=" in the MAGMA code is in fact correct. - N. J. A. Sloane, Feb 02 2009

Crossrefs

Cf. A064230.

Programs

  • Magma
    for a in [1..5] do b := 0; for c in CartesianPower([0,1], a^2) do b +:= Rank(Matrix(a, a, [aa : aa in c])); end for; print b; end for;

Formula

a(n) = Sum_{k=1..n} k * A064230(n,k). - Alois P. Heinz, Jun 18 2022

Extensions

a(6) from Alois P. Heinz, Jun 18 2022

A354741 Triangular array read by rows. T(n,k) is the number of n X n Boolean matrices with row rank k, n >= 0, 0 <= k <= n.

Original entry on oeis.org

1, 1, 1, 1, 9, 6, 1, 49, 306, 156, 1, 225, 8550, 37488, 19272, 1, 961, 194850, 4811700, 17551800, 10995120
Offset: 0

Views

Author

Geoffrey Critzer, Jun 12 2022

Keywords

Comments

Compare to A286331 which counts n X n matrices over the field GF(2). Note that the limit when n->oo of the probability that a matrix over GF(2) has rank n is equal to Product_{i>=1} (1-1/2^i) = 0.288... (see A048651). Here, it appears (from some empirical computations) that the limiting probability that a Boolean matrix has rank n is 1.

Examples

			Table begins:
  1;
  1,   1;
  1,   9,    6;
  1,  49,  306,   156;
  1, 225, 8550, 37488, 19272;
  ...
		

Crossrefs

Columns k = 0 and 1 give A000012, A060867.
Row sums give A002416.

Programs

  • Mathematica
    Table[B = Tuples[Tuples[{0, 1}, nn],nn]; bospan[matrix_]:= Sort[DeleteDuplicates[
         Map[Clip[Total[#]] &, Drop[Subsets[matrix], 1]]]]; rowrank[matrix_] :=
       If[Total[Map[Total, matrix]] == 0, 0, Length[Select[Drop[Subsets[DeleteCases[matrix, Table[0, {nn}]]], 1],
           bospan[#] == bospan[DeleteCases[matrix, Table[0, {nn}]]] &][[ 1]]]]; Tally[
        Table[rowrank[B[[i]]], {i, 1, 2^(nn^2)}]][[All,2]], {nn, 0, 4}] // Grid

Formula

T(n,0) = 1.
T(n,1) = (2^n-1)^2.
T(n,2) = (3^n - 2*2^n + 1)^2 + (1/2)*(4^n - 2*3^n + 2^n)^2.

Extensions

Row n=5 from Pontus von Brömssen, Jul 14 2022

A355333 Triangle read by rows: T(n,k) is the number of n X n Boolean matrices with Schein rank k, 0 <= k <= n.

Original entry on oeis.org

1, 1, 1, 1, 9, 6, 1, 49, 306, 156, 1, 225, 8550, 40656, 16104, 1, 961, 194850, 5771100, 21165720, 6421800
Offset: 0

Views

Author

Pontus von Brömssen, Jun 29 2022

Keywords

Comments

Also, T(n,k) is the number of spanning subgraphs of the complete bipartite graph K_{n,n} that have bipartite dimension (or biclique covering number) k.

Examples

			Triangle begins:
  n\k | 0   1      2       3        4       5
  ----+--------------------------------------
   0  | 1
   1  | 1   1
   2  | 1   9      6
   3  | 1  49    306     156
   4  | 1 225   8550   40656    16104
   5  | 1 961 194850 5771100 21165720 6421800
		

Crossrefs

Cf. A002416 (row sums), A064230, A286331, A354741, A355334.

A173760 Partials sums of A000410.

Original entry on oeis.org

0, 0, 6, 431, 66056, 27960727, 35744362616, 144901919316449
Offset: 1

Views

Author

Jonathan Vos Post, Feb 23 2010

Keywords

Comments

Partials sums of number of singular n X n rational (0,1)-matrices. The subsequence of primes in this partial sum begins: 431.

Examples

			a(8) = 0 + 0 + 6 + 425 + 65625 + 27894671 + 35716401889 + 144866174953833.
		

Crossrefs

Formula

a(n) = SUM[i=0..n] A000410(i).
Showing 1-7 of 7 results.