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A055971
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Numbers k such that k | (sigma(k) - d(k) - phi(k)) and k is not a prime or twice a prime.
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1
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OFFSET
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1,2
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COMMENTS
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LINKS
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MATHEMATICA
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Do[ If[ And[ !PrimeQ[ n ], !PrimeQ[ n/2 ] ], If[ Mod[ DivisorSigma[ 1, n ]-DivisorSigma[ 0, n ]- EulerPhi[ n ], n ]==0, Print[ n ] ] ], {n, 1, 10^8} ]
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PROG
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(PARI) is1(k) = {my(f = factor(k)); !((sigma(f) - numdiv(f) - eulerphi(f)) % k); }
is(k) = !isprime(k) && !(!(k%2) && isprime(k/2)) && is1(k); \\ Amiram Eldar, Apr 29 2024
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CROSSREFS
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KEYWORD
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nonn,more,changed
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AUTHOR
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STATUS
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approved
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