Numbers n such that 5^n-1 has only one primitive prime factor.
1, 2, 3, 4, 6, 7, 8, 10, 11, 12, 13, 18, 24, 28, 47, 48, 49, 56, 57, 88, 90, 92, 108, 110, 116, 120, 127, 134, 141, 149, 161, 171, 181, 198, 202, 206, 236, 248, 288, 357, 384, 420, 458, 500, 530, 536, 619, 620, 694, 798, 897, 929, 981, 992, 1064, 1134, 1230
1
Numbers n such that S000003(n) = 1.
T. D. Noe, Plot of 87 terms
T. D. Noe, Table of 87 terms
Eric W. Weisstein, MathWorld: Primitive Prime Factor
(Mma) d = 5; Select[Range[1000], PrimePowerQ[Cyclotomic[#, d]/GCD[Cyclotomic[#, d], #]] &]
Cf. A161508 (2^n-1 case), S000003, S000360-S000366.
nonn,hard
T. D. Noe, Nov 20 2014