a(n) = lcm(p-1, p+1) where p is the n-th prime.

Terms

a(0) =3a(1) =4a(2) =12a(3) =24a(4) =60a(5) =84a(6) =144a(7) =180a(8) =264a(9) =420a(10) =480a(11) =684a(12) =840a(13) =924a(14) =1104a(15) =1404a(16) =1740a(17) =1860a(18) =2244a(19) =2520a(20) =2664a(21) =3120a(22) =3444a(23) =3960a(24) =4704a(25) =5100a(26) =5304a(27) =5724a(28) =5940a(29) =6384