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A186640 Primes p such that the decimal expansion of 1/p has a periodic part of even length, but are not cyclic numbers (A001913). 1
11, 13, 73, 89, 101, 103, 127, 137, 139, 157, 197, 211, 241, 251, 281, 293, 331, 349, 353, 373, 401, 409, 421, 449, 457, 463, 521, 557, 569, 601, 607, 617, 641, 653, 661, 673, 677, 691, 739, 761, 769, 809, 829, 859, 877, 881, 929, 967, 997, 1009, 1049, 1061 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
FORMULA
p in A028416, but not A001913.
MAPLE
f1_d := proc(n) local st, period:
st := ithprime(n):
period := numtheory[order](10, st):
if (modp(period, 2) = 0) then
if (st-1 <> period) then
RETURN(st):
fi:
fi: end: seq(f1_d(n), n=1..200);
MATHEMATICA
Select[Prime[Range[200]], EvenQ[Length[RealDigits[1/#][[1, 1]]]] && MultiplicativeOrder[10, #] != # - 1 &] (* T. D. Noe, Oct 01 2012 *)
PROG
(PARI) is(p)=if(p>9 && isprime(p), my(o=znorder(Mod(10, p))); o%2==0 && o+1!=p, 0) \\ Charles R Greathouse IV, Oct 01 2012
CROSSREFS
Cf. A028416.
Sequence in context: A132201 A057189 A072580 * A226242 A116436 A185240
KEYWORD
nonn,base
AUTHOR
Jani Melik, Feb 24 2011
STATUS
approved

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Last modified March 28 04:13 EDT 2024. Contains 371235 sequences. (Running on oeis4.)