a(n) = A137505(2n) + A137505(2n+1).

Terms

a(0) =2a(1) =2a(2) =0a(3) =0a(4) =8a(5) =8a(6) =-24a(7) =-24a(8) =104a(9) =104a(10) =-408a(11) =-408a(12) =1640a(13) =1640a(14) =-6552a(15) =-6552a(16) =26216a(17) =26216a(18) =-104856a(19) =-104856a(20) =419432a(21) =419432a(22) =-1677720a(23) =-1677720a(24) =6710888a(25) =6710888a(26) =-26843544a(27) =-26843544a(28) =107374184a(29) =107374184