A186635 - OEIS

A186635

Primes p such that the decimal expansion of 1/p has a periodic part of odd length.

2, 3, 5, 31, 37, 41, 43, 53, 67, 71, 79, 83, 107, 151, 163, 173, 191, 199, 227, 239, 271, 277, 283, 307, 311, 317, 347, 359, 397, 431, 439, 443, 467, 479, 523, 547, 563, 587, 599, 613, 631, 643, 683, 719, 733, 751, 757, 773, 787, 797, 827, 839, 853, 883, 907, 911, 919, 947, 991, 1013, 1031, 1039, 1093, 1123, 1151, 1163, 1187

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OFFSET

1,1

COMMENTS

Interestingly, the initial terms of A040119 (Primes p such that x^4 = 10 has a solution mod p) are identical to the initial terms of this sequence except for 241 which is a term of A040119 but not of A186635. [John W. Layman, Feb 25 2011]

There are many numbers in A040119 that are not here: 241, 641, 769, 809, 1009, 1409, 1601, 1721.... - T. D. Noe, Feb 25 2011

LINKS

Table of n, a(n) for n=1..67.

MAPLE

Ax := proc(n) local st:

st := ithprime(n):

if (modp(numtheory[order](10, st), 2) <> 0) then

RETURN(st)

fi: end: seq(Ax(n), n=1..200);

MATHEMATICA

Union[{2, 5}, Select[Prime[Range[200]], OddQ[Length[RealDigits[1/#][[1, 1]]]] &]]

CROSSREFS