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 A061075 Greatest prime number p(n) with decimal fraction period of length n. 6
 3, 11, 37, 101, 271, 13, 4649, 137, 333667, 9091, 513239, 9901, 265371653, 909091, 2906161, 5882353, 5363222357, 52579, 1111111111111111111, 27961, 10838689, 8779, 11111111111111111111111, 99990001, 182521213001, 1058313049 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Ray Chandler, Table of n, a(n) for n = 1..322 Makoto Kamada, Factorizations of Phi_n(10) FORMULA a(n) = A006530(A019328(n)). - Ray Chandler, May 10 2017 EXAMPLE 1/271 = 0.0036900369, period of n=5 for p(5)=271. MATHEMATICA a[n_] := Cyclotomic[n, 10] // FactorInteger // Last // First; Table[a[n], {n, 1, 26}] (* Jean-François Alcover, Aug 05 2013, after Pari *) PROG (PARI) a(n) = my(p); if(n<1, 0, p=factor(polcyclo(n, 10))[, 1]; p[#p]) CROSSREFS Cf. A003020, A005422, A006530, A007138, A019328. Sequence in context: A007138 A046107 A243110 * A005422 A040017 A007615 Adjacent sequences:  A061072 A061073 A061074 * A061076 A061077 A061078 KEYWORD nonn,nice,base AUTHOR Heiner Muller-Merbach (hmm(AT)sozwi.uni-kl.de), May 29 2001 STATUS approved

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Last modified June 1 13:11 EDT 2020. Contains 334762 sequences. (Running on oeis4.)