%I A056990
%S A056990 2,8,192,22272,11550720,25629327360,236229525504000,8858686914082897920,
%T A056990 1331751782100764385607680
%N A056990 Number of nonsingular n X n (-1,1)-matrices.
%H A056990 Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/
               NonsingularMatrix.html">Link to a section of The World of Mathematics.</
               a>
%Y A056990 Cf. A055165, A056989.
%Y A056990 A056990(n) = 2^(2*n-1) * A055165(n-1).
%Y A056990 Sequence in context: A156526 A009505 A028368 this_sequence A070235 A057194 
               A012539
%Y A056990 Adjacent sequences: A056987 A056988 A056989 this_sequence A056991 A056992 
               A056993
%K A056990 nonn,nice
%O A056990 1,1
%A A056990 Eric Weisstein (eric(AT)weisstein.com)
%E A056990 a(5) from Winston C. Yang (winston(AT)cs.wisc.edu), Aug 26 2000. Further 
               terms computed from A055165 by David desJardins (david(AT)desjardins.org), 
               Apr 22 2001
%E A056990 a(9) from Max Alekseyev, computed from A055165, Jan 15 2007