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A076627
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a(n) = tau(n)*(n-tau(n)), where tau(n) = number of divisors of n (A000005).
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2
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0, 0, 2, 3, 6, 8, 10, 16, 18, 24, 18, 36, 22, 40, 44, 55, 30, 72, 34, 84, 68, 72, 42, 128, 66, 88, 92, 132, 54, 176, 58, 156, 116, 120, 124, 243, 70, 136, 140, 256, 78, 272, 82, 228, 234, 168, 90, 380, 138, 264, 188, 276, 102, 368, 204, 384, 212, 216, 114
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OFFSET
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1,3
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LINKS
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FORMULA
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EXAMPLE
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a(20) = tau(20)*(20-tau(20)) = 6*(20-6) = 84.
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MAPLE
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MATHEMATICA
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#[[1]](#[[2]]-#[[1]])&/@Table[{DivisorSigma[0, n], n}, {n, 60}] (* Harvey P. Dale, May 06 2017 *)
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PROG
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(Haskell)
(PARI) a(n) = my(d = numdiv(n)); d*(n-d); \\ Michel Marcus, Jul 25 2017
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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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