Number of idempotent n X n 0..1 matrices of rank n-2.

Terms

a(0) =0a(1) =1a(2) =27a(3) =282a(4) =2050a(5) =12405a(6) =67557a(7) =344708a(8) =1686132a(9) =8017335a(10) =37383775a(11) =171917790a(12) =782635542a(13) =3535573769a(14) =15875062665a(15) =70921483080a(16) =315457366696