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A280619
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Integers m such that sigma(m) - eulerphi(m) <= 4*sqrt(m).
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1
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1, 2, 3, 4, 5, 7, 8, 9, 11, 13, 17, 19, 23, 25, 29, 31, 37, 41, 43, 47, 49, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 121, 127, 131, 137, 139, 149, 151, 157, 163, 167, 169, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239, 241
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OFFSET
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1,2
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COMMENTS
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Equals {1, 8} union A000430 (primes and square of primes).
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LINKS
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MATHEMATICA
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Select[Range[250], DivisorSigma[1, #]-EulerPhi[#]<=4Sqrt[#]&] (* Harvey P. Dale, Jul 10 2018 *)
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PROG
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(PARI) isok(n) = sigma(n) - eulerphi(n) <= 4*sqrt(n); \\ Michel Marcus, Jan 06 2017
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CROSSREFS
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A000430 is the main entry for this sequence.
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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