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 A216848 #23 Jan 12 2024 01:15:23 %S A216848 7,15,17,21,23,31,33,35,39,41,43,45,47,49,51,55,57,63,65,69,71,73,75, %T A216848 77,79,85,87,89,91,93,95,97,99,103,105,109,111,113,115,117,119,123, %U A216848 127,129,133,135,137,141,143,145,147,151,153,155,157,159,161,165,167 %N A216848 Odd numbers for which 2 is not a primitive root. %H A216848 Amiram Eldar, <a href="/A216848/b216848.txt">Table of n, a(n) for n = 1..10000</a> %t A216848 nn = 200; Select[Range[3, nn, 2], PrimitiveRoot[#] =!= 2 &] (* _T. D. Noe_, Sep 19 2012 *) %o A216848 (PARI) forstep(p=3, 200, 2, if(znorder(Mod(2, p))!=eulerphi(p), print(p))) %Y A216848 Cf. A002326, A001122, A216838. %K A216848 nonn %O A216848 1,1 %A A216848 _V. Raman_, Sep 17 2012