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 A071428 #9 Apr 17 2020 08:21:01 %S A071428 4,6,16,18,28,30,42,52,78,88,100,112,126,136,138,148,162,172,196,198, %T A071428 210,222,232,256,268,280,282,292,316,330,352,378,388,400,448,460,462, %U A071428 486,508,520,556,568,570,592,606,616,630,640,652,676,690,700,738,750 %N A071428 Numbers n such that x^n + x^(n-1) + x^(n-2) + ... + x + 1 is irreducible over GF(3). %C A071428 n such that n+1 is a prime with primitive root 3 (A019334 except for the first term). [_Joerg Arndt_, Jul 05 2011] %o A071428 (PARI) for(n=2,1000,if(polisirreducible(Mod(1,3)*sum(e=0,n,x^e)),print1(n+1,", "))) /* _Joerg Arndt_, Jul 05 2011 */ %o A071428 (PARI) forprime(p=5,1000,if(znorder(Mod(3,p))==p-1,print1(p-1,", "))) /* much faster */ /* _Joerg Arndt_, Jul 05 2011 */ %Y A071428 Cf. A071642. %K A071428 easy,nonn %O A071428 1,1 %A A071428 _Robert G. Wilson v_, Jun 22 2002