Number of 4-turn bishop's tours on an n X n board summed over all starting positions.

Terms

a(0) =0a(1) =0a(2) =24a(3) =328a(4) =1720a(5) =5816a(6) =15424a(7) =34736a(8) =69776a(9) =128528a(10) =221448a(11) =361528a(12) =564872a(13) =850696a(14) =1241968a(15) =1765344a(16) =2451872a(17) =3336864a(18) =4460664a(19) =5868456a(20) =7611096a(21) =9744856a(22) =12332320a(23) =15442064a(24) =19149616a(25) =23537072a(26) =28694120a(27) =34717592a(28) =41712552a(29) =49791784