a(n) = b(n) - Sum_{j=0..n-1} b(j) with b(n) = binomial(2*n, n).

Terms

a(0) =1a(1) =1a(2) =3a(3) =11a(4) =41a(5) =153a(6) =573a(7) =2157a(8) =8163a(9) =31043a(10) =118559a(11) =454479a(12) =1747771a(13) =6740059a(14) =26055459a(15) =100939779a(16) =391785129a(17) =1523230569a(18) =5931153429a(19) =23126146629a(20) =90282147849a(21) =352846964649