a(n) = A127359(n+1)/2 - A127359(n).

Terms

a(0) =1a(1) =3a(2) =10a(3) =33a(4) =110a(5) =366a(6) =1220a(7) =4065a(8) =13550a(9) =45162a(10) =150540a(11) =501786a(12) =1672620a(13) =5575356a(14) =18584520a(15) =61948257a(16) =206494190a(17) =688313490a(18) =2294378300a(19) =7647926046a(20) =25493086820a(21) =84976950468a(22) =283256501560a(23) =944188318938