This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A060261 #12 Oct 03 2021 04:51:59 %S A060261 257,379,811,971,1097,1217,2411,2539,2617,3011,4051,5297,5657,6211, %T A060261 6337,6659,6857,8647,8807,10457,10651,10687,10937,11731,11939,12451, %U A060261 12577,13099,14011,14537,14731,14887,15137,15607,15737,16091,16411 %N 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. %C A060261 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 A060261 Amiram Eldar, <a href="/A060261/b060261.txt">Table of n, a(n) for n = 1..10000</a> %t A060261 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 A060261 The indices of these primes are in A060260. %Y A060261 Cf. A001913, A002371, A060259, A060262. %K A060261 nonn %O A060261 1,1 %A A060261 _Jeff Burch_, Mar 23 2001 %E A060261 Edited by _Dean Hickerson_, Jun 17 2002 %E A060261 Offset corrected by _Amiram Eldar_, Oct 03 2021