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A083255
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Odd composite numbers k such that cototient(k) - phi(k) = k - 2*phi(k) is an odd prime.
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7
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165, 195, 5187, 5865, 7395, 10005, 15045, 16215, 21165, 22695, 27285, 37995, 42585, 44115, 50235, 57885, 59415, 60945, 64005, 310845, 346035, 347565, 486795, 635205, 707115, 890445, 979455, 994755, 1049835, 1070535, 1078815, 1083585, 1121745
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OFFSET
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1,1
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COMMENTS
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Quite a number of terms are divisible by 3*5*17 = 255.
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LINKS
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EXAMPLE
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m = 17425605 = 3*5*23*53*953 is a term since cototient(m) - phi(m) = 9712901 - 8712704 = 197 is an odd prime.
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MATHEMATICA
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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}]
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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