a(n) = (prime(n)^2 - 1)/2 for n >= 2.

Terms

a(0) =4a(1) =12a(2) =24a(3) =60a(4) =84a(5) =144a(6) =180a(7) =264a(8) =420a(9) =480a(10) =684a(11) =840a(12) =924a(13) =1104a(14) =1404a(15) =1740a(16) =1860a(17) =2244a(18) =2520a(19) =2664a(20) =3120a(21) =3444a(22) =3960a(23) =4704a(24) =5100a(25) =5304a(26) =5724a(27) =5940a(28) =6384a(29) =8064