Unique-period primes in base 5, sorted.
3, 7, 13, 31, 313, 521, 601, 5167, 19531, 390001, 12207031, 234750601, 305175781, 152587500001, 59509429687890001, 60081451169922001, 23320317172851318360001, 11735415506748076408140121, 14551915228363037109375001, 9080418348371887359375390001
1
T. D. Noe, Plot of 20 terms
Chris K. Caldwell, Unique prime
(Mma) nn = 1000; t5 = Table[c = Cyclotomic[n, 5]; c/GCD[n, c], {n, 2, nn}]; p5 = Select[t5, PrimePowerQ]; p5 = Table[FactorInteger[i][[1, 1]], {i, p5}]; Take[Sort[p5], 20]
Cf. A040017 (base-10 unique-period primes), A161509 (base 2), A064081.
Cf. S000021.
nonn,base
T. D. Noe, May 14 2014