A060261 - OEIS

A060261

Denoting 5 consecutive primes by p, q, r, s and t, these are the values of q such that q, r and s have 10 as a primitive root, but p and t do not.

%I #12 Oct 03 2021 04:51:59

%S 257,379,811,971,1097,1217,2411,2539,2617,3011,4051,5297,5657,6211,

%T 6337,6659,6857,8647,8807,10457,10651,10687,10937,11731,11939,12451,

%U 12577,13099,14011,14537,14731,14887,15137,15607,15737,16091,16411

%N Denoting 5 consecutive primes by p, q, r, s and t, these are the values of q such that q, r and s have 10 as a primitive root, but p and t do not.

%C A prime p has 10 as a primitive root iff the length of the period of the decimal expansion of 1/p is p-1.

%H Amiram Eldar, <a href="/A060261/b060261.txt">Table of n, a(n) for n = 1..10000</a>

%t test[p_] := MultiplicativeOrder[10, p]===p-1; Prime/@Select[Range[2, 2500], test[Prime[ # ]]&&test[Prime[ #+1]]&&test[Prime[ #+2]]&&!test[Prime[ #-1]]&&!test[Prime[ #+3]]&]

%Y The indices of these primes are in A060260.

%Y Cf. A001913, A002371, A060259, A060262.

%K nonn

%O 1,1

%A _Jeff Burch_, Mar 23 2001

%E Edited by _Dean Hickerson_, Jun 17 2002

%E Offset corrected by _Amiram Eldar_, Oct 03 2021