a(n) = gcd(n!, binomial(2n,n)).

Terms

a(0) =1a(1) =1a(2) =2a(3) =2a(4) =2a(5) =12a(6) =12a(7) =24a(8) =90a(9) =20a(10) =4a(11) =168a(12) =28a(13) =1400a(14) =5400a(15) =720a(16) =90a(17) =5940a(18) =23100a(19) =46200a(20) =180180a(21) =17160a(22) =1560a(23) =140400a(24) =11700a(25) =45864a(26) =179928a(27) =13328a(28) =52360a(29) =5969040