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Talk:Untouchable numbers: Difference between revisions
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I've reduced the number of ranges for counting untouchable numbers. It seems the upper limit for searching for touchable numbers was far higher than I guesstimated. -- [[User:Gerard Schildberger|Gerard Schildberger]] ([[User talk:Gerard Schildberger|talk]]) 09:28, 9 February 2021 (UTC)
== Number of untouchable numbers up to 1 million ==
According to [https://www.numbersaplenty.com/set/untouchable_number/ one of the OEIS links] there are 150,232 untouchable numbers up to 1e6 so it looks like the REXX result (150,233) is off by one here.
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I've managed to isolate the 'awkward' number which is 816,422. The (first) number whose proper divisors sum to this is 19,175,641 its divisors being [1, 29, 151, 841, 4379, 22801, 126991, 661229]. This explains why we need a sieve factor between 19 and 20 to catch it since neither 816,421 or 816,419 is prime. --[[User:PureFox|PureFox]] ([[User talk:PureFox|talk]]) 11:33, 11 February 2021 (UTC)
: That's mighty good detective work ... and a true dedicated ethic. -- [[User:Gerard Schildberger|Gerard Schildberger]] ([[User talk:Gerard Schildberger|talk]]) 11:45, 11 February 2021 (UTC)
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