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 A167791 #42 Nov 10 2023 09:23:55 %S A167791 3,5,9,11,13,19,25,27,29,37,53,59,61,67,81,83,101,107,121,125,131,139, %T A167791 149,163,169,173,179,181,197,211,227,243,269,293,317,347,349,361,373, %U A167791 379,389,419,421,443,461,467,491,509,523,541,547,557,563,587,613,619 %N A167791 Numbers with primitive root 2. %C A167791 Numbers k such that the binary expansion of 1/k has period phi(k). For example 1/27 has a period of 18 bits. %C A167791 All entries are odd. An odd composite number n can have a primitive root if and only if it is a prime power (see A033948). - _V. Raman_, Oct 04 2012 %C A167791 It is unknown whether there is a prime p such that p is in this sequence while p^2 is not. - _Jianing Song_, Jan 27 2019 %H A167791 Amiram Eldar, <a href="/A167791/b167791.txt">Table of n, a(n) for n = 1..10000</a> (terms 1..1000 from Vincenzo Librandi) %t A167791 pr=2; Select[Range[2,2000], MultiplicativeOrder[pr,# ] == EulerPhi[ # ] &] %o A167791 (PARI) for(n=3,200,if(n%2==1&&znorder(Mod(2,n))==eulerphi(n),printf(n","))) \\ _V. Raman_, Oct 04 2012 %o A167791 (PARI) is(n)=n%2 && isprimepower(n) && znorder(Mod(2,n))==eulerphi(n-1) \\ _Charles R Greathouse IV_, Jul 05 2013 %o A167791 (Magma) [n: n in [3..619] | IsPrimitive(2, n)]; // _Arkadiusz Wesolowski_, Dec 22 2020 %Y A167791 Cf. A000010, A001122 (primes with primitive root 2), A033948. %K A167791 nonn %O A167791 1,1 %A A167791 _T. D. Noe_, Nov 12 2009