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 A240102 #7 Nov 26 2014 13:40:42 %S A240102 5,7,23,29,31,37,47,53,61,71,101,103,109,127,149,151,157,167,173,181, %T A240102 191,197,223,239,263,269,271,277,293,317,349,359,367,383,389,397,421, %U A240102 461,479,503,509,529,541,557,607,613,647,653,661,677,701,719,733 %N A240102 Numbers with primitive root -18. %H A240102 Vincenzo Librandi, <a href="/A240102/b240102.txt">Table of n, a(n) for n = 1..1000</a> %t A240102 pr = -18; Select[Range[2, 800], MultiplicativeOrder[pr, #] == EulerPhi[#] &] %o A240102 (PARI) is(n)=if(gcd(n,6)>1, return(0)); my(p=eulerphi(n)); znorder(Mod(-18,n),p)==p \\ _Charles R Greathouse IV_, Nov 26 2014 %Y A240102 Cf. numbers with positive primitive root r: A167791 (r=2), A167792 (r=3), A167793 (r=5), A167794 (r=6), A167795 (r=7), A167796 (r=8), A167797 (r=10), A240028 (r=11), A240030 (r=12), A240032 (r=13), A240094 (r=14), A240096 (r=15), A240101 (r=17), A240103 (r=18). %Y A240102 Cf. numbers with negative primitive root r: A167798 (r=-2), A167799 (r=-3), A167800 (r=-4), A167801 (r=-5), A167802 (r=-6), A167803 (r=-7), A167804 (r=-8), A167805 (r=-9), A167806 (r=-10), A240029 (r=-11), A240031 (r=-12), A240093 (r=-13), A240095 (r=-14), A240097 (r=-15), A240100 (r=-17). %K A240102 nonn,easy %O A240102 1,1 %A A240102 _Vincenzo Librandi_, Apr 01 2014