a(n) = ((2*n + 1)! / n!)^2 / (n + 1).A360602a(n) = ((2*n + 1)! / n!)^2 / (n + 1).Terms a(0) =1a(1) =18a(2) =1200a(3) =176400a(4) =45722880a(5) =18441561600External referencesoeis: A360602