a(n) = binomial(2*n, n) mod binomial(2*n-2, n-1).

Terms

a(0) =0a(1) =2a(2) =10a(3) =42a(4) =168a(5) =660a(6) =2574a(7) =10010a(8) =38896a(9) =151164a(10) =587860a(11) =2288132a(12) =8914800a(13) =34767720a(14) =135727830a(15) =530365050a(16) =2074316640a(17) =8119857900a(18) =31810737420a(19) =124718287980a(20) =489325340400