T(n,k)=Number of idempotent n X n 0..k matrices of rank n-1.

Terms

a(0) =1a(1) =1a(2) =6a(3) =1a(4) =10a(5) =21a(6) =1a(7) =14a(8) =51a(9) =60a(10) =1a(11) =18a(12) =93a(13) =212a(14) =155a(15) =1a(16) =22a(17) =147a(18) =508a(19) =805a(20) =378a(21) =1a(22) =26a(23) =213a(24) =996a(25) =2555a(26) =2910a(27) =889a(28) =1a(29) =30