Number of idempotent 4X4 0..n matrices of rank 3.

Terms

a(0) =60a(1) =212a(2) =508a(3) =996a(4) =1724a(5) =2740a(6) =4092a(7) =5828a(8) =7996a(9) =10644a(10) =13820a(11) =17572a(12) =21948a(13) =26996a(14) =32764a(15) =39300a(16) =46652a(17) =54868a(18) =63996a(19) =74084a(20) =85180a(21) =97332a(22) =110588a(23) =124996a(24) =140604a(25) =157460a(26) =175612a(27) =195108a(28) =215996a(29) =238324