a(n) = Product_{i=0..n} (3*i+1)! / (n+i)!.A036687a(n) = Product_{i=0..n} (3*i+1)! / (n+i)!.Terms a(0) =1a(1) =12a(2) =420a(3) =35280a(4) =6486480a(5) =2473511040External referencesoeis: A036687