Number of ways of placing n non-attacking wazirs on a 3 X n board.

Terms

a(0) =1a(1) =3a(2) =8a(3) =22a(4) =61a(5) =174a(6) =504a(7) =1478a(8) =4374a(9) =13035a(10) =39062a(11) =117585a(12) =355279a(13) =1076845a(14) =3272692a(15) =9969385a(16) =30430982a(17) =93055869a(18) =285013326a(19) =874193006a(20) =2684778104a(21) =8254967674a(22) =25408703236a(23) =78283452265a(24) =241403160254a(25) =745024894092