Number of idempotent 3 X 3 0..n matrices of rank 1.

Terms

a(0) =27a(1) =69a(2) =123a(3) =195a(4) =273a(5) =375a(6) =477a(7) =603a(8) =735a(9) =885a(10) =1035a(11) =1221a(12) =1395a(13) =1593a(14) =1803a(15) =2031a(16) =2253a(17) =2511a(18) =2757a(19) =3039a(20) =3321a(21) =3615a(22) =3909a(23) =4251a(24) =4575a(25) =4917a(26) =5271a(27) =5649a(28) =6015a(29) =6429