a(n) = (2n)!*Sum_{i=1..n} 1/i.A046673a(n) = (2n)!*Sum_{i=1..n} 1/i.Terms a(0) =2a(1) =36a(2) =1320a(3) =84000a(4) =8285760a(5) =1173553920a(6) =226040855040External referencesoeis: A046673