Number of ways to place 4 nonattacking knights on a 4 X n board.

Terms

a(0) =1a(1) =16a(2) =84a(3) =412a(4) =1416a(5) =3640a(6) =7928a(7) =15384a(8) =27352a(9) =45432a(10) =71480a(11) =107608a(12) =156184a(13) =219832a(14) =301432a(15) =404120a(16) =531288a(17) =686584a(18) =873912a(19) =1097432a(20) =1361560a(21) =1670968a(22) =2030584a(23) =2445592a(24) =2921432