Numerator of binomial(2n,n)/(2n+1).

Terms

a(0) =1a(1) =2a(2) =6a(3) =20a(4) =70a(5) =252a(6) =924a(7) =1144a(8) =12870a(9) =48620a(10) =184756a(11) =705432a(12) =2704156a(13) =10400600a(14) =40116600a(15) =155117520a(16) =200360130a(17) =466721244a(18) =9075135300a(19) =11781754600a(20) =137846528820a(21) =538257874440a(22) =140273264248