a(n) = C(2*n,n) / gcd(n,C(2*n,n)).

Terms

a(0) =1a(1) =2a(2) =3a(3) =20a(4) =35a(5) =252a(6) =154a(7) =3432a(8) =6435a(9) =48620a(10) =92378a(11) =705432a(12) =676039a(13) =10400600a(14) =20058300a(15) =10341168a(16) =300540195a(17) =2333606220a(18) =1512522550a(19) =35345263800a(20) =6892326441a(21) =179419291480