Number of idempotent 4 X 4 0..n matrices of rank 1.

Terms

a(0) =108a(1) =404a(2) =892a(3) =1716a(4) =2732a(5) =4324a(6) =6060a(7) =8516a(8) =11308a(9) =14820a(10) =18572a(11) =23668a(12) =28716a(13) =34916a(14) =41836a(15) =49860a(16) =58076a(17) =68164a(18) =78252a(19) =90356a(20) =102988a(21) =116868a(22) =131276a(23) =148564a(24) =165660a(25) =184532a(26) =204604a(27) =226788a(28) =249116a(29) =274900