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A136548
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a(n) = max {k >= 1 | sigma(k) <= n}.
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6
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1, 1, 2, 3, 3, 5, 5, 7, 7, 7, 7, 11, 11, 13, 13, 13, 13, 17, 17, 19, 19, 19, 19, 23, 23, 23, 23, 23, 23, 29, 29, 31, 31, 31, 31, 31, 31, 37, 37, 37, 37, 41, 41, 43, 43, 43, 43, 47, 47, 47, 47, 47, 47, 53, 53, 53, 53, 53, 53, 59, 59, 61, 61, 61, 61, 61, 61, 67, 67, 67, 67, 71, 71
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OFFSET
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1,3
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COMMENTS
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Old name was "Extended 'previous prime' version 2".
This is the same as A151799 if n >= 3 and falls back to 1, if no prime smaller than n exists.
For every k >= 1, the equation n - a(n) = k has infinitely many solutions. - Bernard Schott, Mar 05 2019
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REFERENCES
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P. Tauvel, Exercices d'Algèbre Générale et d'Arithmétique, Dunod, 2004, Exercice 18 p. 204.
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LINKS
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FORMULA
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For n > 1, a(n) < n. If p is prime, a(p+1) = p. - Bernard Schott, Mar 05 2019
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MATHEMATICA
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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