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 A379642 #11 Feb 27 2025 11:16:18
%S A379642 2,5,7,41,11,73,547,17,19,1181,23,6481,398581,29,31,21523361,103,
%T A379642 530713,1597,42521761,43,5501,47,97,151,53,109,430697,59,47763361,683,
%U A379642 926510094425921,25411,956353,71,282429005041,18427,5301533,79,14401,83,2857,431,89
%N A379642 Smallest primitive prime factor of 9^n-1.
%C A379642 Also, smallest prime p such that 1/p has nonary period n.
%H A379642 Max Alekseyev, <a href="/A379642/b379642.txt">Table of n, a(n) for n = 1..730</a> (first 690 terms from Sean A. Irvine)
%o A379642 (PARI) listap(nn) = {prf = []; for (n=1, nn, vp = (factor(9^n-1)[, 1])~; f = setminus(Set(vp), Set(prf)); prf = concat(prf, f); print1(vecmin(Vec(f)), ", "); ); }
%Y A379642 Cf. A112927 (base 2), A143663 (base 3), A112092 (base 4), A143665 (base 5), A379639 (base 6), A379640 (base 7), A379641 (base 8), A379642 (base 9), A007138 (base 10), A379644 (base 11), A252170 (base 12).
%Y A379642 Cf. A274909.
%K A379642 nonn
%O A379642 1,1
%A A379642 _Sean A. Irvine_, Dec 28 2024