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%I #71 Apr 03 2021 08:43:05
%S 81,121,343,361,529,649,841,961,1219,1331,1537,1633,1837,1849,1909,
%T 1969,2047,2209,2401,2497,2773,2809,2959,3113,3127,3151,3223,3421,
%U 3481,3487,3841,3901,3953,4189,4321,4399,4531,4661,4741,4829,4897,4913,5041,5129,5137,5191,5269,5401,5539,5753
%N Composite numbers k such that phi(x) = phi(k) has only 2 solutions: x = k and x = 2*k.
%C All terms are odd.
%C If q > 7 is in A005385, then q^2 is in the sequence.
%C The sequence has a positive natural density. - Information from Carl Pomerance, Jan 07 2017
%H Amiram Eldar, <a href="/A280587/b280587.txt">Table of n, a(n) for n = 1..10000</a>
%Y Cf. A000010, A005385, A058340 (such primes).
%K nonn
%O 1,1
%A _Thomas Ordowski_ and _Altug Alkan_, Jan 06 2017
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