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A179887
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Nonprimes q such that antiharmonic mean B(q) of the numbers k < q such that gcd(k, q) = 1 is integer, where B(q) = A053818(q) / A023896(q) = A175505(q) / A175506(q).
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20
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1, 10, 22, 34, 46, 55, 58, 82, 85, 91, 94, 106, 110, 115, 118, 133, 142, 145, 166, 170, 178, 182, 187, 202, 205, 214, 217, 226, 230, 235, 247, 253, 259, 262, 265, 266, 274, 290, 295, 298, 301, 319, 334, 346, 355, 358, 374, 382, 391, 394, 403, 410, 415, 427
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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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EXAMPLE
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a(6) = 55 because B(55) = A053818(55) / A023896(55) = 40700 / 1100 = 37 (integer).
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MATHEMATICA
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f[n_] := 2 Plus @@ (Select[ Range@n, GCD[ #, n] == 1 &]^2)/(n*EulerPhi@n); Select[ Range@ 433, ! PrimeQ@# && IntegerQ@ f@# &] (* Robert G. Wilson v, Aug 02 2010 *)
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CROSSREFS
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Cf. A179871, A179872, A179873, A179874, A179875, A179876, A179877, A179878, A179879, A179880, A179882, A179883, A179884, A179885, A179887, A179890, A179891.
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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