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, 440334654777631, 121499449, 77843839397

Offset: 1

Author

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

Keywords

• nonn
• nice
• base

Examples

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

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

Crossrefs

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

Last terms in rows of A046107.

Programs

Mathematica

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

PARI

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

Formula

a(n) = A006530(A019328(n)). - Ray Chandler, May 10 2017

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