%I #4 Mar 30 2012 17:40:41
%S 0,4,32,512,15872,907008,104535552
%N Number of symmetric singular n X n (+1,-1) matrices over the reals.
%F a(n) = 2^(n*(n+1)/2) - A118994(n) - A118997(n) [From _Max Alekseyev_, May 08 2009]
%Y Cf. A086906, A119010, A057982, A118992.
%K nonn,more
%O 1,2
%A _Giovanni Resta_, May 08 2006