T(n,k) = Number of idempotent n X n -k..k matrices.

Terms

a(0) =2a(1) =2a(2) =12a(3) =2a(4) =28a(5) =164a(6) =2a(7) =44a(8) =848a(9) =5712a(10) =2a(11) =60a(12) =1928a(13) =102432a(14) =407072a(15) =2a(16) =76a(17) =3752a(18) =462464