Number of ways to place 2 nonattacking knights on an n X n board.

Terms

a(0) =0a(1) =6a(2) =28a(3) =96a(4) =252a(5) =550a(6) =1056a(7) =1848a(8) =3016a(9) =4662a(10) =6900a(11) =9856a(12) =13668a(13) =18486a(14) =24472a(15) =31800a(16) =40656a(17) =51238a(18) =63756a(19) =78432a(20) =95500a(21) =115206a(22) =137808a(23) =163576a(24) =192792a(25) =225750a(26) =262756a(27) =304128a(28) =350196a(29) =401302