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

Terms

a(0) =1a(1) =12a(2) =36a(3) =100a(4) =233a(5) =456a(6) =796a(7) =1280a(8) =1935a(9) =2788a(10) =3866a(11) =5196a(12) =6805a(13) =8720a(14) =10968a(15) =13576a(16) =16571a(17) =19980a(18) =23830a(19) =28148a(20) =32961a(21) =38296a(22) =44180a(23) =50640a(24) =57703a(25) =65396a(26) =73746a(27) =82780a(28) =92525a(29) =103008