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 A377939 #6 Nov 11 2024 22:26:20 %S A377939 3,5,7,17,19,22,23,29,31,33,37,43,47,53,55,71,85,87,89,91,102,103,105, %T A377939 106,109,111,112,113,115,116,117,122,123,133,139,141,143,145,149,153, %U A377939 155,157,162,163,167,175,177,191,193,199,201,203,209,211,221,223,233,239,241,243,245,247,249,253 %N A377939 Nonsquares k such that A377938(k) is not a prime. %C A377939 Numbers k such that k is a primitive root modulo some nonprime x > k but not modulo any prime between k and x. %C A377939 Numbers k such that 0 < A377938(k) < A023049(k). %H A377939 Robert Israel, <a href="/A377939/b377939.txt">Table of n, a(n) for n = 1..10000</a> %e A377939 a(3) = 7 is a term because 7 is a primitive root mod 10, while the least prime > 7 for which 7 is a primitive root is 11. %p A377939 filter:= proc(n) local k; %p A377939 if issqr(n) then return false fi; %p A377939 for k from n+1 do %p A377939 if igcd(k,n) = 1 and numtheory:-order(n,k) = numtheory:-phi(k) then return not isprime(k) fi %p A377939 od %p A377939 end proc: %p A377939 select(filter, [$2..1000]); %Y A377939 Cf. A023049, A377938. %K A377939 nonn %O A377939 1,1 %A A377939 _Robert Israel_, Nov 11 2024