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%I #5 Dec 28 2024 16:18:47
%S 2,5,7,41,11,73,547,17,19,1181,23,6481,398581,29,31,21523361,103,
%T 530713,1597,42521761,43,5501,47,97,151,53,109,430697,59,47763361,683,
%U 926510094425921,25411,956353,71,282429005041,18427,5301533,79,14401,83,2857,431,89
%N Smallest primitive prime factor of 9^n-1.
%C Also, smallest prime p such that 1/p has nonary period n.
%H Sean A. Irvine, <a href="/A379642/b379642.txt">Table of n, a(n) for n = 1..690</a>
%o (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 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 Cf. A274909.
%K nonn
%O 1,1
%A _Sean A. Irvine_, Dec 28 2024