a(n) = Sum_{i=1..floor((n+1)/4)} a(2*i-1) * a(n-2*i+1), with a(1)=a(3)=2 and a(2)=1.

Terms

a(0) =2a(1) =1a(2) =2a(3) =4a(4) =8a(5) =16a(6) =40a(7) =96a(8) =224a(9) =528a(10) =1376a(11) =3520a(12) =8864a(13) =22272a(14) =59648a(15) =156992a(16) =407808a(17) =1060864a(18) =2872960a(19) =7701504a(20) =20460032a(21) =54299904a(22) =148601856a(23) =402977792a(24) =1084414464a(25) =2918055936a(26) =8035600384a(27) =21980652544a(28) =59769698304a(29) =162381037568