a(n) = C_n / 2 if n is even or ( C_n + C_((n-1)/2) ) / 2 if n is odd, where C = Catalan numbers (A000108).

A007595

a(n) = C_n / 2 if n is even or ( C_n + C_((n-1)/2) ) / 2 if n is odd, where C = Catalan numbers (A000108).

Terms

    a(0) =1a(1) =1a(2) =3a(3) =7a(4) =22a(5) =66a(6) =217a(7) =715a(8) =2438a(9) =8398a(10) =29414a(11) =104006a(12) =371516a(13) =1337220a(14) =4847637a(15) =17678835a(16) =64823110a(17) =238819350a(18) =883634026a(19) =3282060210a(20) =12233141908a(21) =45741281820a(22) =171529836218a(23) =644952073662

External references