2^(n-1)J(n,1/2) where J(n,x)=n-th Jacobsthal polynomial.

Terms

a(0) =0a(1) =1a(2) =2a(3) =6a(4) =32a(5) =28a(6) =248a(7) =120a(8) =1504a(9) =496a(10) =8096a(11) =2016a(12) =40704a(13) =8128a(14) =195968a(15) =32640a(16) =915968a(17) =130816a(18) =4190720a(19) =523776a(20) =18866176a(21) =2096128a(22) =83867648a(23) =8386560a(24) =369057792a(25) =33550336a(26) =1610522624a(27) =134209536a(28) =6979125248a(29) =536854528