Number of idempotent 4X4 0..n matrices of rank 2.

Terms

a(0) =282a(1) =1434a(2) =4182a(3) =9762a(4) =19110a(5) =34602a(6) =56982a(7) =89766a(8) =134298a(9) =194262a(10) =271074a(11) =371478a(12) =494346a(13) =647358a(14) =833226a(15) =1057542a(16) =1321482a(17) =1636314a(18) =1999926a(19) =2425794a(20) =2913678a(21) =3472242a(22) =4104942a(23) =4828626