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 A060257 #18 Mar 14 2022 17:27:11 %S A060257 4,7,8,9,10,15,17,18,25,29,30,32,35,39,41,42,44,48,50,51,55,56,57,65, %T A060257 68,73,75,76,77,81,84,89,93,94,95,96,97,100,105,106,108,114,118,120, %U A060257 126,127,129,132,141,142,143,148,150,154,159,160,162,164,165,166,171 %N A060257 Numbers k such that 1/prime(k) has period prime(k) - 1. %H A060257 Amiram Eldar, <a href="/A060257/b060257.txt">Table of n, a(n) for n = 1..10000</a> %H A060257 Matt Parker and Brady Haran, <a href="https://www.youtube.com/watch?v=DmfxIhmGPP4">The Reciprocals of Primes</a>, Numberphile video (2022) %F A060257 a(n) = PrimePi(A001913(n)). - _Alexander Adamchuk_, Jan 28 2007 %t A060257 Select[Range[200], MultiplicativeOrder[10, (p = Prime[#])] == p - 1 &] (* _Amiram Eldar_, Oct 03 2021 *) %Y A060257 Cf. A060258. %Y A060257 Cf. A000720 (PrimePi), A001913 (primes with primitive root 10). %K A060257 nonn %O A060257 1,1 %A A060257 _Jeff Burch_, Mar 22 2001