a(1) = 1; for n > 1, a(n) = prime root of n-th prime power (A000961).

Terms

a(0) =1a(1) =2a(2) =3a(3) =2a(4) =5a(5) =7a(6) =2a(7) =3a(8) =11a(9) =13a(10) =2a(11) =17a(12) =19a(13) =23a(14) =5a(15) =3a(16) =29a(17) =31a(18) =2a(19) =37a(20) =41a(21) =43a(22) =47a(23) =7a(24) =53a(25) =59a(26) =61a(27) =2a(28) =67a(29) =71