a(n) = Sum_{k=0..floor(n/3)} 2^k * 3^(n-3*k) * binomial(k+6,6) * binomial(2*k,2*(n-3*k)).

Terms

a(0) =1a(1) =0a(2) =0a(3) =14a(4) =42a(5) =0a(6) =112a(7) =2016a(8) =1008a(9) =672a(10) =30240a(11) =90720a(12) =21504a(13) =282240a(14) =2116800a(15) =2554944a(16) =2268000a(17) =27941760a(18) =83884416a(19) =65596608a(20) =267043392a(21) =1475544576a(22) =2431021824a(23) =2927232000a(24) =17853158400a(25) =53704594944a(26) =66020258304a(27) =180793733120a(28) =803074162176