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A033885
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a(n) = 3*n - sum of divisors of n.
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6
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2, 3, 5, 5, 9, 6, 13, 9, 14, 12, 21, 8, 25, 18, 21, 17, 33, 15, 37, 18, 31, 30, 45, 12, 44, 36, 41, 28, 57, 18, 61, 33, 51, 48, 57, 17, 73, 54, 61, 30, 81, 30, 85, 48, 57, 66, 93, 20, 90, 57, 81, 58, 105, 42, 93, 48, 91, 84, 117, 12, 121, 90, 85, 65, 111, 54, 133, 78, 111, 66
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OFFSET
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1,1
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COMMENTS
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The first zero term occurs at n=120. The first negative term is a(180) = -6. For any k, k*n - sigma(n) is negative for some n. See A023199. - T. D. Noe, Aug 07 2003
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LINKS
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Ivan Neretin, Table of n, a(n) for n = 1..10000
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FORMULA
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a(n) = A008585(n) - A000203(n). - Omar E. Pol, Sep 30 2017
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EXAMPLE
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For n=4, 3n=12, sum of divisors of n is 1+2+4=7, so a(4)=12-7=5.
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MAPLE
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with(numtheory): for n from 1 to 150 do printf(`%d, `, 3*n-sigma(n)) od:
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MATHEMATICA
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Table[3 n - DivisorSigma[1, n], {n, 70}] (* Ivan Neretin, Sep 30 2017 *)
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PROG
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(PARI) a(n)=3*n-sigma(n) \\ Charles R Greathouse IV, Mar 16 2016
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CROSSREFS
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Cf. A000203, A008585, A023199.
Sequence in context: A138181 A006447 A014237 * A053079 A158901 A096736
Adjacent sequences: A033882 A033883 A033884 * A033886 A033887 A033888
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KEYWORD
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sign
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AUTHOR
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N. J. A. Sloane
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EXTENSIONS
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More terms from James A. Sellers, Jun 01 2000
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STATUS
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approved
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