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A226647
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Numbers k such that Sum_{i=1..k} sigma(i) is divisible by Sum_{i=1..k} d(i), where sigma(i) = sum of divisors of i (A000203), and d(i) = number of divisors of i (A000005).
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6
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OFFSET
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1,2
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COMMENTS
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The ratio corresponding to a(6) is 4249100789716352394810 / 1807894350282 = 2350303705. a(7) > 10^12. - Giovanni Resta, Apr 13 2017
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LINKS
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FORMULA
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EXAMPLE
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A006218(9) = 23, A024916(9) = 69, 23 divides 69, so 9 is in the sequence.
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MATHEMATICA
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Flatten[Position[Accumulate[Table[{DivisorSigma[1, n], DivisorSigma[0, n]}, {n, 100}]], _?(Divisible[First[#], Last[#]]&), {1}, Heads->False]] (* Harvey P. Dale, Jun 19 2013 *)
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PROG
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(PARI) isok(n) = sum(k=1, n, sigma(k)) % sum(k=1, n, numdiv(k)) == 0; \\ Michel Marcus, Jul 07 2016
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CROSSREFS
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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