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A211779
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a(n) = Sum_{d_<n | n} sigma(d_<n), where d_<n = divisors of n that are less than n, sigma(x) = A000203(x).
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6
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0, 1, 1, 4, 1, 8, 1, 11, 5, 10, 1, 27, 1, 12, 11, 26, 1, 33, 1, 35, 13, 16, 1, 70, 7, 18, 18, 43, 1, 68, 1, 57, 17, 22, 15, 107, 1, 24, 19, 92, 1, 84, 1, 59, 48, 28, 1, 161, 9, 59, 23, 67, 1, 112, 19, 114, 25, 34, 1, 217, 1, 36, 58, 120, 21, 116, 1, 83, 29
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OFFSET
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1,4
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COMMENTS
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The numbers n < 1000 such that n divides a(n) are 4, 10, 42, and 90. (See A224488).
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LINKS
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FORMULA
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Sum_{k=1..n} a(k) ~ c * n^2, where c = Pi^4/72 - Pi^2/12 = 0.530437... . - Amiram Eldar, Mar 17 2024
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MATHEMATICA
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Table[Sum[DivisorSigma[1, d], {d, Most[Divisors[n]]}], {n, 100}] (* T. D. Noe, Apr 26 2012 *)
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PROG
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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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