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A256562
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Number of deficient numbers <= n.
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2
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1, 2, 3, 4, 5, 5, 6, 7, 8, 9, 10, 10, 11, 12, 13, 14, 15, 15, 16, 16, 17, 18, 19, 19, 20, 21, 22, 22, 23, 23, 24, 25, 26, 27, 28, 28, 29, 30, 31, 31, 32, 32, 33, 34, 35, 36, 37, 37, 38, 39, 40, 41, 42, 42, 43, 43, 44, 45, 46, 46, 47, 48, 49, 50, 51, 51, 52, 53
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OFFSET
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1,2
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LINKS
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FORMULA
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a(n) ~ c*n, where c = 0.752380... is the asymptotic density of the deficient numbers (A318172). - Amiram Eldar, Mar 21 2021
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EXAMPLE
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For k=1 to 5, all numbers are deficients so a(k) = k in this range.
a(6) = 5 since 6 is the first number that is not deficient.
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MATHEMATICA
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a[n_]:=Length[Select[Range[n], DivisorSigma[1, #]/#<2&]]; a/@Range[68] (* Ivan N. Ianakiev, Apr 03 2015 *)
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PROG
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(PARI) a(n) = sum(k=1, n, sigma(k)/k < 2);
(Magma) [#[k:k in [1..n]| DivisorSigma(1, k) lt 2*k]:n in [1..70]]; // Marius A. Burtea, Nov 06 2019
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CROSSREFS
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Cf. A091194 (number of abundant numbers <= n).
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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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