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A083243
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n is in the sequence iff number of numbers unrelated to n is smaller than that of related ones[=divisors and coprimes] to n: A045763[n] < A073757[n] or A045763[n]<n/2 or A073757[n]>n/2.
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9
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1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 55, 56, 57, 58, 59, 61, 62, 63, 64, 65, 67, 68, 69, 71, 73, 74, 75, 76, 77, 79
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OFFSET
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1,2
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LINKS
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Table of n, a(n) for n=1..72.
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FORMULA
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d[n]+phi[n]-1<n/2
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EXAMPLE
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n=146 is here because it has d=4 divisors,r=72 numbers are coprimes
and u=71 are unrelated: d+r-1=4+72-1=75>n/2=146/2=73>71=u.
n=61455 is here because has 16 divisors and equal number of
coprimes and unrelated numbers u=r=30720: d+r-1-30735>30720.
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MATHEMATICA
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Do[r=EulerPhi[n]; d=DivisorSigma[0, n]; u=n-r-d+1; If[Greater[n-u, n/2], Print[n, {d, r, u}]], {n, 1, 100}]
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CROSSREFS
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Cf. A000005, A000010, A045763, A073757, A020488, A083244, A083245.
Sequence in context: A179797 A044923 A180925 * A002837 A056561 A174670
Adjacent sequences: A083240 A083241 A083242 * A083244 A083245 A083246
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KEYWORD
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nonn
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AUTHOR
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Labos E. (labos(AT)amna1.sote.hu), May 07 2003
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STATUS
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approved
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