a(n) = p^4*(p-1), where p = prime(n).

Terms

a(0) =16a(1) =162a(2) =2500a(3) =14406a(4) =146410a(5) =342732a(6) =1336336a(7) =2345778a(8) =6156502a(9) =19803868a(10) =27705630a(11) =67469796a(12) =113030440a(13) =143589642a(14) =224465326a(15) =410305012a(16) =702806938a(17) =830750460a(18) =1329973986a(19) =1778817670a(20) =2044673352a(21) =3038106318a(22) =3891582322