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Greatest prime number p(n) with decimal fraction period of length n.
8

%I #29 Apr 26 2022 18:41:04

%S 3,11,37,101,271,13,4649,137,333667,9091,513239,9901,265371653,909091,

%T 2906161,5882353,5363222357,52579,1111111111111111111,27961,10838689,

%U 8779,11111111111111111111111,99990001,182521213001,1058313049

%N Greatest prime number p(n) with decimal fraction period of length n.

%H <a href="/A061075/b061075.txt">Table of n, a(n) for n = 1..352</a>

%H Makoto Kamada, <a href="https://stdkmd.net/nrr/repunit/phin10.htm">Factorizations of Phi_n(10)</a>

%H <a href="/index/1#1overn">Index entries for sequences related to decimal expansion of 1/n</a>

%F a(n) = A006530(A019328(n)). - _Ray Chandler_, May 10 2017

%e 1/271 = 0.0036900369, period of n=5 for p(5)=271.

%t a[n_] := Cyclotomic[n, 10] // FactorInteger // Last // First; Table[a[n], {n, 1, 26}] (* _Jean-François Alcover_, Aug 05 2013, after Pari *)

%o (PARI) a(n) = my(p); if(n<1, 0, p=factor(polcyclo(n,10))[,1]; p[#p])

%Y Cf. A003020, A005422, A006530, A007138, A019328.

%K nonn,nice,base

%O 1,1

%A Heiner Muller-Merbach (hmm(AT)sozwi.uni-kl.de), May 29 2001

%E Terms to a(322) in b-file from _Ray Chandler_, Apr 28 2017

%E a(323)-a(352) in b-file from _Max Alekseyev_, Apr 26 2022