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 A379640 #11 Feb 27 2025 11:04:34
%S A379640 2,1,19,5,2801,43,29,1201,37,11,1123,13,16148168401,113,31,17,14009,
%T A379640 117307,419,281,11898664849,23,47,73,2551,53,109,13564461457,59,
%U A379640 6568801,311,353,3631,29078814248401,2127431041,13841169553,223,351121,486643,41,83,51031
%N A379640 Smallest primitive prime factor of 7^n-1.
%C A379640 Also, smallest prime p such that 1/p has septimal period n.
%H A379640 Max Alekseyev, <a href="/A379640/b379640.txt">Table of n, a(n) for n = 1..430</a> (first 388 terms from Sean A. Irvine)
%o A379640 (PARI) listap(nn) = {prf = []; for (n=1, nn, vp = (factor(7^n-1)[, 1])~; f = setminus(Set(vp), Set(prf)); prf = concat(prf, f); print1(vecmin(Vec(f)), ", "); ); }
%Y A379640 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 A379640 Cf. A074249.
%K A379640 nonn
%O A379640 1,1
%A A379640 _Sean A. Irvine_, Dec 28 2024