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 A301913 #33 May 04 2018 22:41:36 %S A301913 5,7,11,17,19,29,31,43,53,59,79,83,89,97,101,107,113,127,131,137,139, %T A301913 149,163,173,179,197,199,211,223,227,233,241,251,257,269,281,283,293, %U A301913 317,331,337,347,353,379,389,401,409,419,439,443,449,457,461,463,467 %N A301913 Primes which divide numbers of the form 3^k + 2 for k >= 1. %C A301913 The first odd prime not to appear in the sequence is 3 because 3^k + 2 == 2 mod 3 for k >= 1. %C A301913 Primes p such that the order of -2 (mod p) divides the order of 3 (mod p). - _Joerg Arndt_, Mar 31 2018, corrected by _Robert Israel_, May 04 2018 %H A301913 Robert Israel, <a href="/A301913/b301913.txt">Table of n, a(n) for n = 1..10000</a> %e A301913 5 divides 245 which is 3^5+2 so 5 is in the sequence. %e A301913 7 divides 245 which is 3^5+2 so 7 is in the sequence. %e A301913 The values of x = (3^k+2) mod 13 for k = 0, 1, 2, 3, ... are 3, 5, 11, 3, 5, 11, ...; 13 never divides any 3^k + 2, so 13 is not in the sequence. %p A301913 select(t -> numtheory:-mlog(-2,3,t)<>FAIL, [seq(ithprime(i),i=3..100)]); %t A301913 fQ[p_] := IntegerQ@ MultiplicativeOrder[3, p, -2]; Select[ Prime@ Range@ 100, fQ] (* _Robert G. Wilson v_, Apr 07 2018 *) %o A301913 (PARI) is(n)=n>4 && isprime(n) && znorder(Mod(-2,n))%znorder(Mod(3,n))==0 \\ _Charles R Greathouse IV_, May 04 2018 %Y A301913 Cf. A168607. %K A301913 nonn %O A301913 1,1 %A A301913 _Luke W. Richards_, Mar 28 2018