Numbers n such that 9^n-1 has only one primitive prime factor.
1, 2, 4, 6, 10, 12, 16, 18, 20, 30, 32, 36, 54, 64, 66, 118, 138, 152, 182, 232, 264, 336, 340, 380, 414, 446, 492, 540, 624, 720, 762, 1066, 1094, 1098, 1170, 1230, 1254, 1320, 1428, 1546, 2018, 2574, 2724, 2804, 2920, 3074, 3316, 3646, 4124, 4132, 4186
1
Numbers n such that S000007(n) = 1.
T. D. Noe, Plot of 58 terms
T. D. Noe, Table of 58 terms
Eric W. Weisstein, MathWorld: Primitive Prime Factor
(Mma) d = 9; Select[Range[1000], PrimePowerQ[Cyclotomic[#, d]/GCD[Cyclotomic[#, d], #]] &]
Cf. A161508 (2^n-1 case), S000007, S000360-S000365.
nonn,hard
T. D. Noe, Nov 20 2014