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A326692
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Values of n for which the denominator of (Sum_{prime p | n} 1/p - 1/n) is n.
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3
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1, 4, 8, 9, 15, 16, 20, 24, 25, 27, 28, 32, 33, 35, 36, 40, 44, 45, 49, 51, 52, 60, 63, 64, 65, 68, 69, 72, 76, 77, 81, 85, 87, 88, 91, 92, 95, 96, 99, 100, 104, 108, 112, 115, 116, 117, 119, 121, 123, 124, 125, 128, 133, 135, 136, 140, 141, 143, 144, 145, 148
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OFFSET
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1,2
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COMMENTS
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Any prime power p^k with k > 1 is a term, as 1/p - 1/p^k = (p^(k-1) - 1)/p^k which is in reduced form and has denominator p^k.
Are there infinitely many Carmichael numbers A002997 in the sequence?
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LINKS
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FORMULA
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EXAMPLE
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1/3 + 1/5 - 1/15 = 7/15 has denominator 15, so 15 is a term.
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MATHEMATICA
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PrimeFactors[n_] := Select[Divisors[n], PrimeQ];
f[n_] := Denominator[Sum[1/p, {p, PrimeFactors[n]}] - 1/n];
Select[Range[148], f[#] == # &]
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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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