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 1-10 of 13 results. Next

A051753 Number of n X n (-1,0,1)-matrices having maximum determinant (=A003433(n)).

Original entry on oeis.org

1, 4, 240, 384, 30720, 7372800
Offset: 1

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Author

Keywords

Comments

This count includes equivalent matrices.

Crossrefs

Cf. A003433.

Extensions

a(4) from Jud McCranie, Oct 15 2000
a(5) from Giovanni Resta, Feb 20 2009
a(1)-a(5) confirmed and a(6) added by Minfeng Wang, May 29 2024

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

A133465 Erroneous version of A003433.

Original entry on oeis.org

1, 2, 4, 16, 44, 160, 576, 4096, 14336, 73728, 327680, 2985984, 14929920, 77635584
Offset: 1

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Author

Keywords

References

  • W. D. Smith, "9 Open Problems", 6th Computational Geometry Day, Nov 13 1987.

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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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

A084109 n is congruent to 1 (mod 4) and is not the sum of two squares.

Original entry on oeis.org

21, 33, 57, 69, 77, 93, 105, 129, 133, 141, 161, 165, 177, 189, 201, 209, 213, 217, 237, 249, 253, 273, 285, 297, 301, 309, 321, 329, 341, 345, 357, 381, 385, 393, 413, 417, 429, 437, 453, 465, 469, 473, 489, 497
Offset: 1

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Author

William P. Orrick, Jun 18 2003

Keywords

Comments

Alternatively, n is congruent to 1 (mod 4) with at least 2 distinct prime factors congruent to 3 (mod 4) in the squarefree part of n. - Comment corrected by Jean-Christophe Hervé, Oct 25 2015
Applications to the theory of optimal weighing designs and maximal determinants: An (n+1) X (n+1) conference matrix is impossible.
The upper bound of Ehlich/Wojtas on the determinant of a (0,1) matrix of order congruent to 1 (mod 4) cannot be achieved for n X n matrices.
The bound of Ehlich/Wojtas on the determinant of a (-1,1) matrix of order congruent to 2 (mod 4) cannot be achieved for (n+1) X (n+1) matrices.
Numbers with only odd prime factors, of which a strictly positive even number are raised to an odd power and congruent to 3 (mod 4). - Jean-Christophe Hervé, Oct 24 2015

Examples

			a(1) = 3*7 = 21, a(2) = 3*11 = 33, a(3) = 3*19 = 57, a(14) = 3^3*7 = 189.
		

References

  • F. J. MacWilliams and N. J. A. Sloane, The Theory of Error-Correcting Codes, Elsevier-North Holland, 1978, p. 56.

Crossrefs

Programs

  • Maple
    N:= 1000: # to get all entries <= N
    S:= {seq(i,i=1..N,4)} minus
       {seq(seq(i^2+j^2, j=1..floor(sqrt(N-i^2)),2),i=0..floor(sqrt(N)),2)}:
    sort(convert(S,list)); # Robert Israel, Oct 25 2015
  • Mathematica
    a[m_] := Complement[Range[1, m, 4], Union[Flatten[Table[j^2+k^2, {j, 1, Sqrt[m], 2}, {k, 0, Sqrt[m], 2}]]]]
  • PARI
    is(n)=if(n%4!=1, return(0)); my(f=factor(n)); for(i=1, #f~, if(f[i, 1]%4==3 && f[i, 2]%2, return(1))); 0 \\ Charles R Greathouse IV, Jul 01 2016

A119003 Maximal determinant of real n X n symmetric (+1,-1) matrices.

Original entry on oeis.org

1, 0, 4, 16, 48, 160, 576, 4096, 14336, 65536
Offset: 1

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Author

Giovanni Resta, May 08 2006

Keywords

Comments

Computation of the determinant of these two matrices:
{-1, -1, -1, -1, 1, 1, 1, -1},
{-1, 1, -1, 1, 1, 1, -1, 1},
{-1, -1, 1, 1, 1, -1, -1, -1},
{-1, 1, 1, 1, -1, 1, 1, -1},
{ 1, 1, 1, -1, 1, 1, -1, -1},
{ 1, 1, -1, 1, 1, -1, 1, -1},
{ 1, -1, -1, 1, -1, 1, -1, -1},
{-1, 1, -1, -1, -1, -1, -1, -1}
and
{-1, 1, 1, -1, 1, -1, 1, 1, 1},
{ 1, -1, 1, -1, 1, 1, 1, 1, -1},
{ 1, 1, 1, 1, 1, -1, -1, 1, -1},
{-1, -1, 1, 1, -1, 1, 1, -1, 1},
{ 1, 1, 1, -1, -1, -1, 1, -1, -1},
{-1, 1, -1, 1, -1, 1, 1, 1, -1},
{ 1, 1, -1, 1, 1, 1, 1, -1, 1},
{ 1, 1, 1, -1, -1, 1, -1, 1, 1},
{ 1, -1, -1, 1, -1, -1, 1, 1, 1}
shows that a(8) = A003433(8) = 4096 and a(9) = A003433(9) = 14336. - Jean-François Alcover, Nov 19 2017
a(n) = n^(n/2) once there exists a symmetric Hadamard matrix of order n. In particular, a(12) = 12^6, a(16) = 16^8, etc. - Max Alekseyev, Jun 17 2025

Crossrefs

Extensions

a(8) and a(9) from Jean-François Alcover, Nov 19 2017
a(10) from Max Alekseyev, Jun 17 2025

A215723 Maximum determinant of an n X n circulant (1,-1)-matrix.

Original entry on oeis.org

1, 0, 4, 16, 48, 128, 512, 2304, 6912, 22528, 273408, 2097152, 14929920, 50331648, 390905856, 1644167168, 12279939072, 69660573696, 865782202368, 5566277615616, 41248865910784, 215055782117376, 2385859554836480, 25783171861708800, 146322302697472000, 1107244165160239104, 11063259546716733440, 76787161889935196160
Offset: 1

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Author

W. Edwin Clark, Aug 22 2012

Keywords

Comments

a(n) is divisible by 2^(n-1), see A215897. [Joerg Arndt, Aug 26 2012]

References

  • Warren D. Smith, Posting to the Math Fun Mailing List August 18, 2012.

Crossrefs

Cf. A003433, A086432 (same for circulant (0,1) matrices), A215724 (same for (1,-1)-Toeplitz matrices).
Cf. A215897 ( =a(n)/2^(n-1) ).

Programs

  • Maple
    a:=proc(n)
    local T, b, U, M,d,r;
    T:= combinat:-cartprod([seq({-1, 1}, j = 1 .. n)]);
    b:= 0;
    while not T[finished] do
       U := T[nextvalue]();
       M := Matrix(n, shape = Circulant[U]);
       d:= LinearAlgebra:-Determinant(M):
       if d > b then b := d; end if;
    end do;
    return b;
    end proc:
  • PARI
    a(n)={my(m=0); for(p=n>1, 2^(n-1)-1, m=max(m, matdet(matrix(n, n, i, j, 1-2*bittest(p, (i-j)%n))))); m} /* For illustrative purpose only: becomes slow for n>15 */ /* M. F. Hasler, Aug 25 2012 */

Extensions

a(16)-a(22) from Joerg Arndt, Aug 25 2012
a(23)-a(28) (as calculated by Warren Smith) from W. Edwin Clark, Sep 02 2012

A111368 The number of maximal determinant {-1,1} matrices of order n.

Original entry on oeis.org

1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 5, 3, 3, 3, 3, 7
Offset: 1

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Author

William P. Orrick, Nov 08 2005

Keywords

Comments

The number of inequivalent maximal determinant {-1,1} matrices of order n where two matrices are considered equivalent if one can be obtained from the other by permuting rows, permuting columns and multiplying rows or columns by -1. Additional terms: a(24)=60, a(25)=78, a(28)=487. The terms a(4n) are given in sequence A007299.

Crossrefs

Extensions

Added a(19)-a(21) and Brent et al. reference.
Edited by William P. Orrick, Dec 20 2011

A215644 Full spectrum threshold for maximal determinant {+1, -1} matrices: largest order of submatrix for which the full spectrum of absolute determinant values occurs.

Original entry on oeis.org

1, 1, 2, 2, 3, 4, 6, 4, 6, 6, 7, 6, 7, 7, 7, 8, 8, 8, 9, 8, 10
Offset: 1

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Keywords

Comments

a(n) is the maximum of m(A) taken over all maximal determinant matrices A of order n, where m(A) is the maximum m such that the full spectrum of possible values (ignoring sign) occurs for the minors of order m of A.

Examples

			For n = 8 we have a(8) = 4 as a Hadamard matrix of order 8 has minors of order 4 with the full spectrum of values {0,8,16} (signs are ignored) but minors of order m > 4 do not have this property.
		

Crossrefs

Extensions

We calculated the first 21 terms of the sequence by an exhaustive computation of minors of known maximal determinant matrices as at August 2012.

A094813 a(n) = number of (0,1) matrices of size n X n whose determinants are k, where -L <= k <= +L and L = A003432(n).

Original entry on oeis.org

1, 13, 10, 33, 84, 338, 84, 360, 1200, 10020, 42976, 10020, 12003600, 42795, 145485, 1206772, 4848581, 21059938, 4848585, 1206796, 145473, 42807, 3600
Offset: 1

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Author

Patricia J. Egan (capdevcom(AT)lycos.com), Jun 11 2004

Keywords

Examples

			n = 2 : det([a b];[c d]) is (ad - bc) [16 possible matrices]
0 if ((a OR d) = zero) AND ((b OR c) = zero)
OR ((a AND d) = one) AND ((b AND D) = one) [10 possible matrices]
+1 if ((a AND d) = one) AND ((b OR c) = zero) [ 3 possible matrices]
-1 if ((a OR d) = zero) AND ((b AND c) = one) [ 3 possible matrices]
		

Crossrefs

Showing 1-10 of 13 results. Next