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%I #27 Feb 13 2024 14:40:40
%S 7,17,23,41,47,71,79,97,103,137,167,191,193,199,239,263,271,311,313,
%T 359,367,383,401,409,449,463,479,487,503,521,569,599,607,647,719,743,
%U 751,761,769,809,823,839,857,863,887,929,967,977,983,991,1009,1031
%N Primes p such that the multiplicative order of 2 modulo p is (p-1)/2.
%C It appears that this is also the sequence of values of n for which the sum of terms of one period of the base-2 MR-expansion (see A136042) of 1/n equals (n-1)/2. An example appears in A155072 where one period of the base-2 MR-expansion of 1/17 is shown to be {5,1,1,1) with sum 8=(17-1)/2. [_John W. Layman_, Jan 19 2009]
%H Klaus Brockhaus, <a href="/A115591/b115591.txt">Table of n, a(n) for n=1..1000</a>
%t fQ[n_] := 1 + 2 MultiplicativeOrder[2, n] == n; Select[ Prime@ Range@ 174, fQ]
%o (Magma) [ p: p in PrimesUpTo(1031) | r eq 1 and Order(R!2) eq q where q,r is Quotrem(p,2) where R is ResidueClassRing(p) ]; // _Klaus Brockhaus_, Dec 02 2008
%o (PARI) r=2;forprime(p=3,1500,z=(p-1)/znorder(Mod(r,p));if(z==2,print1(p,", "))); \\ _Joerg Arndt_, Jan 12 2011
%Y Cf. A001122, A001133.
%Y Cf. A136042, A155072. [_John W. Layman_, Jan 19 2009]
%K nonn
%O 1,1
%A _Don Reble_, Mar 11 2006
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