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A161509 The unique primitive prime factor of 2^n-1 for the n in A161508. 5

%I #9 Feb 10 2024 23:17:01

%S 3,7,5,31,127,17,73,11,13,8191,43,151,257,131071,19,524287,41,337,683,

%T 241,2731,262657,331,2147483647,65537,599479,43691,174763,61681,5419,

%U 2796203,4432676798593,87211,15790321,2305843009213693951,715827883

%N The unique primitive prime factor of 2^n-1 for the n in A161508.

%C For these primes p, the binary expansion of 1/p has a unique period length. The binary analog of A007615.

%H Max Alekseyev, <a href="/A161509/b161509.txt">Table of n, a(n) for n = 1..179</a> (terms for n=1..100 from T. D. Noe)

%t Reap[Do[c=Cyclotomic[n,2]; q=c/GCD[c,n]; If[PrimePowerQ[q], Sow[FactorInteger[q][[1,1]]]],{n,100}]][[2,1]]

%Y Cf. A144755 (sorted).

%K nonn

%O 1,1

%A _T. D. Noe_, Jun 17 2009

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Last modified February 28 21:38 EST 2024. Contains 370400 sequences. (Running on oeis4.)