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

Terms

a(0) =1a(1) =70a(2) =406a(3) =1168a(4) =2948a(5) =6576a(6) =13122a(7) =23808a(8) =40168a(9) =63996a(10) =97344a(11) =142516a(12) =202072a(13) =278828a(14) =375856a(15) =496484a(16) =644296a(17) =823132a(18) =1037088a(19) =1290516a(20) =1588024a(21) =1934476a(22) =2334992a(23) =2794948a(24) =3319976