Least k > 2 such that (n^k - 1)/(n-1) is prime, or 0 if no such prime exists.

Terms

a(0) =3a(1) =3a(2) =0a(3) =3a(4) =3a(5) =5a(6) =3a(7) =0a(8) =19a(9) =17a(10) =3a(11) =5a(12) =3a(13) =3a(14) =0a(15) =3a(16) =25667a(17) =19a(18) =3a(19) =3a(20) =5a(21) =5a(22) =3a(23) =0a(24) =7a(25) =3a(26) =5a(27) =5a(28) =5a(29) =7