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A286002
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a(n) = 2n - d(n), where d(n) is the number of divisors of n (A000005).
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1
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1, 2, 4, 5, 8, 8, 12, 12, 15, 16, 20, 18, 24, 24, 26, 27, 32, 30, 36, 34, 38, 40, 44, 40, 47, 48, 50, 50, 56, 52, 60, 58, 62, 64, 66, 63, 72, 72, 74, 72, 80, 76, 84, 82, 84, 88, 92, 86, 95, 94, 98, 98, 104, 100, 106, 104, 110, 112, 116
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OFFSET
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1,2
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COMMENTS
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Let H_n denote the y=n/x (1<=x<=n) piece of the hyperbola. a(n) is the number of intersections between H_n and the Cartesian grid (Z X R union R X Z) and a(n)-1 is the number of (a,a+1) X (b,b+1) open unit squares, with a and b integers, crossed by H_n.
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LINKS
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FORMULA
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MAPLE
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MATHEMATICA
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PROG
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(PARI) a(n) = 2*n - numdiv(n)
(Magma) [2*n - NumberOfDivisors(n): n in [1..100]]; // Vincenzo Librandi, Jun 12 2017
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CROSSREFS
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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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