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%I #21 Mar 25 2021 04:52:41
%S 165,195,5187,5865,7395,10005,15045,16215,21165,22695,27285,37995,
%T 42585,44115,50235,57885,59415,60945,64005,310845,346035,347565,
%U 486795,635205,707115,890445,979455,994755,1049835,1070535,1078815,1083585,1121745
%N Odd composite numbers k such that cototient(k) - phi(k) = k - 2*phi(k) is an odd prime.
%C Quite a number of terms are divisible by 3*5*17 = 255.
%H Amiram Eldar, <a href="/A083255/b083255.txt">Table of n, a(n) for n = 1..10000</a> (terms 1..369 from R. J. Mathar)
%e m = 17425605 = 3*5*23*53*953 is a term since cototient(m) - phi(m) = 9712901 - 8712704 = 197 is an odd prime.
%t Do[s=EulerPhi[n]; c=n-s; If[Greater[c, s]&&PrimeQ[c-s]&&OddQ[c-s]&&!PrimeQ[n], Print[{n, c-s, n/255}]], {n, 1, 10000000}]
%Y Cf. A000010, A051953, A036798, A067800, A083254.
%K nonn
%O 1,1
%A _Labos Elemer_, May 08 2003
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