Number of ways to place 3 nonattacking nightriders on a 3 X n board.

Terms

a(0) =1a(1) =12a(2) =36a(3) =100a(4) =213a(5) =408a(6) =712a(7) =1148a(8) =1745a(9) =2528a(10) =3524a(11) =4760a(12) =6263a(13) =8060a(14) =10178a(15) =12644a(16) =15485a(17) =18728a(18) =22400a(19) =26528a(20) =31139a(21) =36260a(22) =41918a(23) =48140a(24) =54953a(25) =62384a(26) =70460a(27) =79208a(28) =88655a(29) =98828