%I A056989
%S A056989 2,48,11808,27947520,609653621760
%N A056989 Number of nonsingular n X n (-1,0,1)-matrices (over the reals).
%H A056989 Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/
               NonsingularMatrix.html">Link to a section of The World of Mathematics.</
               a>
%H A056989 <a href="Sindx_Mat.html#binmat">Index entries for sequences related to 
               binary matrices</a>
%F A056989 It would be nice to have an estimate for the asymptotic rate of growth.
%e A056989 a(1) = 2: [1], [ -1].
%e A056989 a(2) = 48: There are 8 choices for the first column, u (say) and then 
               the 2nd column can be anything except 0, u, -u, so 6 choices, giving 
               a total of 8*6 = 48.
%Y A056989 Cf. A055165, A053290, A056990; A055165, A002884, A046747.
%Y A056989 Sequence in context: A053071 A002820 A053290 this_sequence A090770 A081960 
               A123742
%Y A056989 Adjacent sequences: A056986 A056987 A056988 this_sequence A056990 A056991 
               A056992
%K A056989 nonn,nice,more
%O A056989 1,1
%A A056989 Eric Weisstein (eric(AT)weisstein.com)
%E A056989 a(4) from Winston C. Yang (winston(AT)cs.wisc.edu), Aug 27 2000
%E A056989 Entry revised by N. J. A. Sloane (njas(AT)research.att.com), Jan 02 2007
%E A056989 a(5) from Giovanni Resta (g.resta(AT)iit.cnr.it), Feb 20 2009