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 A098268 #11 Jul 17 2013 04:57:24
%S A098268 2,2,0,4,2,2,6,32,2,4,62,20,210,2,8,22,4096,2570,2,6,9198,3084,258,18,
%T A098268 96,121574,4,28,10,162,2,6,62,3230,563940,2,104592,2,44,23091222
%N A098268 Unique prime factors of 2^n+1 are of the form kn+1. These are the values for k.
%C A098268 The values for 2^n+1 are in A000051. In this sequence where a(n) has more than one k value they are separated with commas. See A097406 & A097407.
%o A098268 (PARI) isprimitivep(p, n) = {for (r=1, n-1, if (((2^r+1) % p) == 0, return (0));); return (1);}
%o A098268 lista(n) = {f = factor(2^n+1); hasprim = 0;for(i=1, #f~, if (isprimitivep(f[i, 1], n), hasprim = 1; print1((f[i, 1]-1)/n, ", "););); if (! hasprim, print1(0, ", "));} \\ _Michel Marcus_, Jul 16 2013
%K A098268 nonn
%O A098268 1,1
%A A098268 _Marco Matosic_, Sep 01 2004