a(n+1) = a(n) * (a(n-1) + 1).A005831a(n+1) = a(n) * (a(n-1) + 1).Terms a(0) =0a(1) =1a(2) =1a(3) =2a(4) =4a(5) =12a(6) =60a(7) =780a(8) =47580a(9) =37159980External referencesoeis: A005831