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

Terms

a(0) =0a(1) =6a(2) =28a(3) =96a(4) =240a(5) =518a(6) =980a(7) =1712a(8) =2784a(9) =4310a(10) =6380a(11) =9136a(12) =12688a(13) =17206a(14) =22820a(15) =29728a(16) =38080a(17) =48102a(18) =59964a(19) =73920a(20) =90160a(21) =108966a(22) =130548a(23) =155216a(24) =183200a(25) =214838a(26) =250380a(27) =290192a(28) =334544a(29) =383830