T(n,k)=Number of idempotent n X n -k..k matrices of rank 1.

Terms

a(0) =1a(1) =1a(2) =10a(3) =1a(4) =26a(5) =87a(6) =1a(7) =42a(8) =447a(9) =740a(10) =1a(11) =58a(12) =999a(13) =6820a(14) =6285a(15) =1a(16) =74a(17) =1935a(18) =20708