Q. about {0,1}-matrices.

[Artur]

P.S.
Sample 2 x 2:
For case 2 x 2 we have only 2 different characteristic polynomials with  
frequences:
1  x^2-x-1   Golois S2 = C2
3  x^2-2x+1  Reducible
__
4
Will be interesting later do sequences with frequency of different Galois  
Tranzitive Groups


ARTUR

Dnia 06-01-2007 o 03:47:54 N. J. A. Sloane <njas at research.att.com>  
napisał(a):

> Dear MathFun, SeqFans:
>
> Could anyone extend this sequence?
>
> %I A125587
> %S A125587 1,4,68,5008
> %N A125587 Call an n X n matrix robust if the top left i X i submatrix  
> is invertible for all i = 1...n. Sequence gives number of n X n robust  
> real {0,1}-matrices.
> %e A125587 a(2) = 4:
> %e A125587 10 10 11 11
> %e A125587 01 11 01 10
> %O A125587 1,2
> %Y A125587 Cf. A125586.
> %K A125587 nonn,more
> %A A125587 njas and Vinay Vaishampayan (vinay(AT)research.att.com), Jan  
> 05 2007
>
> This "robust" property is relevant when doing an LU decomposition
> of a matrix, so it may have a more official name (besides "all principal
> submatrices are nonsingular", I mean).
>
> Neil
>
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>