a(n) = Sum_{k=0..floor(n/2)} 2^k * binomial(2*k+1,2*n-4*k+1).

Terms

a(0) =1a(1) =0a(2) =6a(3) =2a(4) =20a(5) =40a(6) =60a(7) =280a(8) =312a(9) =1352a(10) =2368a(11) =5856a(12) =15632a(13) =28864a(14) =86048a(15) =168096a(16) =434496a(17) =1002752a(18) =2234560a(19) =5649536a(20) =12211840a(21) =30328960a(22) =68791296a(23) =161430528a(24) =383891712a(25) =874668032a(26) =2099908096a(27) =4817531392a(28) =11379016704a(29) =26596497408