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

Terms

a(0) =1a(1) =6a(2) =26a(3) =86a(4) =211a(5) =426a(6) =758a(7) =1234a(8) =1881a(9) =2726a(10) =3796a(11) =5118a(12) =6719a(13) =8626a(14) =10866a(15) =13466a(16) =16453a(17) =19854a(18) =23696a(19) =28006a(20) =32811a(21) =38138a(22) =44014a(23) =50466a(24) =57521a(25) =65206a(26) =73548a(27) =82574a(28) =92311a(29) =102786