A061075 - OEIS

A061075

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

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

Table of n, a(n) for n = 1..352

Makoto Kamada, Factorizations of Phi_n(10)

Index entries for sequences related to decimal expansion of 1/n

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

EXTENSIONS

Terms to a(322) in b-file from Ray Chandler, Apr 28 2017

a(323)-a(352) in b-file from Max Alekseyev, Apr 26 2022

STATUS

approved