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%I #17 Jun 14 2022 02:28:06
%S 1,3,7,9,11,13,17,19,21,23,27,29,31,33,37,43,47,49,51,53,57,59,61,63,
%T 67,69,71,73,77,79,81,83,87,89,91,93,97,99,101,103,107,109,111,113,
%U 119,121,127,129,131,133,137,139,141,143,147,149,151,153,157,159,161,163
%N k/10 when gcd(k, 2^k+1) = 5.
%C The number of terms not exceeding 10^m, for m = 1, 2, ..., are 4, 38, 371, 3726, 37259, 372542, 3725411, 37254006, 372539990, ... . Apparently, the asymptotic density of this sequence exists and equals 0.3725... . - _Amiram Eldar_, Jun 14 2022
%H Amiram Eldar, <a href="/A069254/b069254.txt">Table of n, a(n) for n = 1..10000</a>
%t Select[Range[170], GCD[10*#, PowerMod[2, 10*#, 10*#] + 1] == 5 &] (* _Amiram Eldar_, Jun 14 2022*)
%o (PARI) lista(nn) = select(x->(gcd(x, 2^x+1) == 5), [1..nn])/10 \\ _Michel Marcus_, Oct 27 2019
%Y Cf. A069226.
%K easy,nonn
%O 1,2
%A _Benoit Cloitre_, Apr 13 2002
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