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A046522
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a(n) = 2*floor(sqrt(n)) - d(n), where d(n) is the number of divisors of n (A000005).
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6
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1, 0, 0, 1, 2, 0, 2, 0, 3, 2, 4, 0, 4, 2, 2, 3, 6, 2, 6, 2, 4, 4, 6, 0, 7, 6, 6, 4, 8, 2, 8, 4, 6, 6, 6, 3, 10, 8, 8, 4, 10, 4, 10, 6, 6, 8, 10, 2, 11, 8, 10, 8, 12, 6, 10, 6, 10, 10, 12, 2, 12, 10, 8, 9, 12, 8, 14, 10, 12, 8, 14, 4, 14, 12, 10, 10, 12, 8, 14, 6
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OFFSET
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1,5
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COMMENTS
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Always >= 0.
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REFERENCES
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D. S. Mitrinovic et al., Handbook of Number Theory, Kluwer, Section II.1.1.
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LINKS
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MAPLE
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with(numtheory); f := n->2*floor(sqrt(n))-sigma[ 0 ](n);
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MATHEMATICA
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Table[2Floor[Sqrt[n]]-DivisorSigma[0, n], {n, 80}] (* Harvey P. Dale, Nov 27 2013 *)
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PROG
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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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STATUS
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approved
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