STATUS
reviewed
approved
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Revision History for A140221
(Bold, blue-underlined text is an addition; faded, red-underlined text is aShowing entries 1-10 | older changes
A number n is included if n is coprime to Sum_{k=1..n} d(k), where d(k) is the number of divisors of k.
(history; published version)
(history; published version)
STATUS
proposed
reviewed
STATUS
editing
proposed
MATHEMATICA
With[{r = Range[200]}, PositionIndex[CoprimeQ[r, Accumulate[DivisorSigma[0, r]]]][True]] (* Paolo Xausa, Feb 21 2024 *)
STATUS
approved
editing
LINKS
Robert Israel, <a href="/A140221/b140221_1.txt">Table of n, a(n) for n = 1..10000</a>
STATUS
reviewed
approved
STATUS
proposed
reviewed
STATUS
editing
proposed
NAME
A number n is included if n is coprime to sumSum_{k=1 to ..n} d(k), where d(k) is the number of divisors of k.
COMMENTS
sumSum_{k=1 to ..n} d(k) = sumSum_{k=1 to ..n} floor(n/k) = A006218(n).
STATUS
proposed
editing
STATUS
editing
proposed