A118990 - OEIS

The OEIS is supported by the many generous donors to the OEIS Foundation.

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

Other ways to Give

A118990

Number of symmetric singular n X n (+1,-1) matrices over the reals.

%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