A060257 - OEIS

A060257

Numbers k such that 1/prime(k) has period prime(k) - 1.

4, 7, 8, 9, 10, 15, 17, 18, 25, 29, 30, 32, 35, 39, 41, 42, 44, 48, 50, 51, 55, 56, 57, 65, 68, 73, 75, 76, 77, 81, 84, 89, 93, 94, 95, 96, 97, 100, 105, 106, 108, 114, 118, 120, 126, 127, 129, 132, 141, 142, 143, 148, 150, 154, 159, 160, 162, 164, 165, 166, 171

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000

Matt Parker and Brady Haran, The Reciprocals of Primes, Numberphile video (2022)

FORMULA

a(n) = PrimePi(A001913(n)). - Alexander Adamchuk, Jan 28 2007

MATHEMATICA

Select[Range[200], MultiplicativeOrder[10, (p = Prime[#])] == p - 1 &] (* Amiram Eldar, Oct 03 2021 *)

CROSSREFS

Cf. A060258.