Number of ways to place 2n nonattacking kings on a vertical cylinder 4 X 2n.

Terms

a(0) =8a(1) =32a(2) =100a(3) =276a(4) =708a(5) =1732a(6) =4100a(7) =9476a(8) =21508a(9) =48132a(10) =106500a(11) =233476a(12) =507908a(13) =1097732a(14) =2359300a(15) =5046276a(16) =10747908a(17) =22806532a(18) =48234500a(19) =101711876a(20) =213909508a(21) =448790532a(22) =939524100a(23) =1962934276a(24) =4093640708a(25) =8522825732a(26) =17716740100a(27) =36775657476a(28) =76235669508