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 1-6 of 6 results.

A003432 Hadamard maximal determinant problem: largest determinant of a (real) {0,1}-matrix of order n.

Original entry on oeis.org

1, 1, 1, 2, 3, 5, 9, 32, 56, 144, 320, 1458, 3645, 9477, 25515, 131072, 327680, 1114112, 3411968, 19531250, 56640625, 195312500
Offset: 0

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Author

Keywords

Comments

The entries are restricted to 0 and 1; the determinant is computed in the field of real numbers.
Suppose M = (m(i,j)) is an n X n matrix of real numbers. Let
a(n) = max det M subject to m(i,j) = 0 or 1 [this sequence],
g(n) = max det M subject to m(i,j) = -1 or 1 [A003433],
h(n) = max det M subject to m(i,j) = -1, 0 or 1 [A003433],
F(n) = max det M subject to 0 <= m(i,j) <= 1 [this sequence],
G(n) = max det M subject to -1 <= m(i,j) <= 1 [A003433].
Then a(n) = F(n), g(n) = h(n) = G(n), g(n) = 2^(n-1)*a(n-1). Thus all five problems are equivalent.
Hadamard proved that a(n) <= 2^(-n)*(n+1)^((n+1)/2), with equality if and only if a Hadamard matrix of order n+1 exists. Equivalently, g(n) <= n^(n/2), with equality if and only if a Hadamard matrix of order n exists. It is believed that a Hadamard matrix of order n exists if and only if n = 1, 2 or a multiple of 4 (see A036297).
We have a(21) = 195312500?, a(22) = 662671875?, and a(36) = 1200757082375992968. Furthermore, starting with a(23), many constructions are known that attain the upper bounds of Hadamard, Barba, and Ehlich-Wojtas, and are therefore maximal. See the Orrick-Solomon web site for further information. [Edited by William P. Orrick, Dec 20 2011]
The entry a(21) = 195312500 is now known to be correct. [Edited by Richard P. Brent, Aug 17 2021]

Examples

			G.f. = 1 + x + x^2 + 2*x^3 + 3*x^4 + 5*x^5 + 9*x^6 + 32*x^7 + 56*x^8 + ...
One of 2 ways to get determinant 9 with a 6 X 6 matrix, found by Williamson:
  1 0 0 1 1 0
  0 0 1 1 1 1
  1 1 1 0 0 1
  0 1 0 1 0 1
  0 1 0 0 1 1
  0 1 1 1 1 0
		

References

  • J. Hadamard, Résolution d'une question relative aux déterminants, Bull. des Sciences Math. 2 (1893), 240-246.
  • F. J. MacWilliams and N. J. A. Sloane, The Theory of Error-Correcting Codes, Elsevier-North Holland, 1978, p. 54.
  • N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Crossrefs

A003433(n) = 2^(n-1)*a(n-1). Cf. A013588, A036297, A051752.

Extensions

a(18)-a(20) added by William P. Orrick, Dec 20 2011
a(21) added by Richard P. Brent, Aug 16 2021

A086264 Number of real {0,1} n X n matrices having determinant=1.

Original entry on oeis.org

1, 1, 3, 84, 10020, 4851360, 9240051240, 67745781734400, 1883481284085791040
Offset: 0

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Author

Hugo Pfoertner, Oct 05 2003

Keywords

Crossrefs

Programs

  • Mathematica
    a[n_] := Module[{M, iter, cnt = 0}, M = Table[a[i, j], {i, 1, n}, {j, 1, n}]; iter = Thread[{Flatten[M], 0, 1}]; Do[If[Det[M] == 1, cnt++], Evaluate[Sequence @@ iter]]; cnt];
    Do[Print[n, " ", a[n]], {n, 1, 4}] (* Jean-François Alcover, Dec 09 2018 *)

Extensions

a(0)=1 prepended by Alois P. Heinz, Jun 18 2022
a(7) from Minfeng Wang, Feb 09 2023
a(8) from Minfeng Wang, Apr 26 2024

A089478 Triangle T(n,k) read by rows, where T(n,k) = number of times the determinant of a real n X n (0,1)-matrix takes the value k, for n >= 0, 0 <= k <= A003432(n).

Original entry on oeis.org

0, 1, 1, 1, 10, 3, 338, 84, 3, 42976, 10020, 1200, 60, 21040112, 4851360, 1213920, 144720, 43560, 3600, 39882864736, 9240051240, 3868663680, 768723480, 418703040, 63612360, 46569600, 6438600, 5014800, 529200, 292604283435872
Offset: 0

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Author

Hugo Pfoertner, Nov 04 2003

Keywords

Comments

The first 4 rows were provided by Wouter Meeussen.

Examples

			a(4) = T(2,1) = 3 because there are 3 different (0,1)-matrices with determinant=1:
  ((1,0),(0,1)), ((1,1),(0,1)), ((1,0),(1,1)).
Triangle T(n,k) begins:
         0,       1;
         1,       1;
        10,       3;
       338,      84,       3;
     42976,   10020,    1200,     60;
  21040112, 4851360, 1213920, 144720, 43560, 3600;
  ...
		

Crossrefs

Cf. T(n,0) = A046747(n), T(n,1) = A086264(n), T(n,A003432(n)) = A051752(n).
The n-th row of the table contains A089472(n) nonzero entries.
Cf. A089479.

Programs

Extensions

Edited by Alois P. Heinz, Dec 20 2023

A119004 Number of n X n real symmetric (0,1)-matrices having maximal determinant (=A119002(n)).

Original entry on oeis.org

1, 1, 1, 18, 160, 900, 2520, 36960, 393120, 15573600
Offset: 1

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Author

Giovanni Resta, May 08 2006

Keywords

Crossrefs

Extensions

a(8)-a(10) from Max Alekseyev, Jun 17 2025

A188895 Number of n X n (real) {-1,1}-matrices having determinant A003433(n).

Original entry on oeis.org

1, 4, 96, 384, 30720, 7372800, 4335206400, 2477260800, 25684239974400, 7191587192832000
Offset: 0

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Author

Eric W. Weisstein, Apr 19 2011

Keywords

Crossrefs

Formula

a(n) = 2^(2n+1) * A051752(n) for n>=2. - Hugo Pfoertner and Minfeng Wang, Jan 22 2023

Extensions

Offset changed to 0 by Hugo Pfoertner, Jan 23 2023
a(5)-a(9) from Minfeng Wang, Jan 22 2023

A052655 a(2) = 6, otherwise a(n) = n*n!.

Original entry on oeis.org

0, 1, 6, 18, 96, 600, 4320, 35280, 322560, 3265920, 36288000, 439084800, 5748019200, 80951270400, 1220496076800, 19615115520000, 334764638208000, 6046686277632000, 115242726703104000, 2311256907767808000
Offset: 0

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Author

encyclopedia(AT)pommard.inria.fr, Jan 25 2000

Keywords

Comments

a(n) = number of real non-singular (0,1)-matrices of order n having maximal permanent = A000255(n). Proof: [W. Edwin Clark and Richard Brualdi] The maximum permanent is per A where A has all 1's except for n-1 0's on the main diagonal. By Corollary 4.4 in the Brualdi et al. reference for n >= 4 any n X n (0,1)-matrix B with per B = per A can be obtained from A by permuting rows and columns. Since there are n ways to place the single 1 on the main diagonal and then n! ways to permute the distinct rows, a(n) = n*n! if n >=4. Direct computation shows this also holds for n = 1 and 3. - W. Edwin Clark, Nov 15 2003

Examples

			a(2)=6 because there are 6 (0,1)-matrices with nonzero determinant having permanent=1. See example in A089482. The (0,1)-matrix with maximal permanent=2 ((1,1),(1,1)) has det=0.
		

Crossrefs

Cf. A000255. A089480 gives occurrence counts for permanents of non-singular (0, 1)-matrices, A051752 number of (0, 1)-matrices with maximal determinant A003432.
Essentially the same as A001563.

Programs

  • Maple
    spec := [S,{S=Prod(Z,Union(Z,Prod(Sequence(Z),Sequence(Z))))},labeled]: seq(combstruct[count](spec,size=n), n=0..20);
  • Mathematica
    Join[{0,1,6},Table[n*n!,{n,3,20}]] (* Harvey P. Dale, Apr 20 2012 *)

Formula

E.g.f.: x*(-2*x^2+x^3+x+1)/(-1+x)^2.
Showing 1-6 of 6 results.