a(n) is the number of invertible 2 X 2 upper triangular matrices over Z_p where p = prime(n).

Terms

a(0) =2a(1) =12a(2) =80a(3) =252a(4) =1100a(5) =1872a(6) =4352a(7) =6156a(8) =11132a(9) =22736a(10) =27900a(11) =47952a(12) =65600a(13) =75852a(14) =99452a(15) =143312a(16) =198476a(17) =219600a(18) =291852a(19) =347900a(20) =378432a(21) =480636a(22) =558092a(23) =689216a(24) =893952a(25) =1010000a(26) =1071612a(27) =1202252a(28) =1271376a(29) =1417472