Timeline for Numbers whose digits, in order, display prime factors
Current License: CC BY-SA 4.0
14 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Sep 18, 2022 at 15:58 | comment | added | IronEagle | Checking up to 2^31 still reveals no solutions. | |
| Jan 30, 2021 at 1:08 | comment | added | IronEagle | Code crashed at around 249,000,000 with nothing found. My guess is that if found, it will be analytically, not numerically. I'm probably stopping my efforts here, if someone else wants to try numerically my code is at github.com/AD-Wright/StrongLobsters | |
| Jan 29, 2021 at 3:45 | comment | added | IronEagle | If you're interested in the substring, rather than subsequence, version where repeats are allowed, it's oeis.org/A050694 | |
| Jan 28, 2021 at 17:58 | comment | added | IronEagle | It actually helps if you're trying to find a solution numerically, because you can just compare the list of prime factors with the sorted digits of the number itself: if they are not identical, it's not a solution. No need to generate substrings, etc. | |
| Jan 28, 2021 at 17:55 | comment | added | Carl Witthoft | @IronEagle I suppose I could modify the problem so you can re-use digits for different primes, e.g. use "23" for 2, 3, and 23 . | |
| Jan 28, 2021 at 17:33 | comment | added | IronEagle | Thinking about it a bit, I believe that a composite number can have at most the same number of digits as its prime factors combined, so the multiset of the digits of the number would have to be equal to the multiset of the digits of all the prime factors. i.e. you can't have a bigger or smaller number of digits in the number than you have in the combined prime factors. Don't know if that helps at all. | |
| Jan 28, 2021 at 16:03 | comment | added | IronEagle | I wrote a program to check for this condition, and I think the logic is correct; I've checked up to 520,000 overnight and haven't found any matching numbers yet. Don't know how one would go about a proof of existence/nonexistence. Maybe something with the factors, the numbers, and a matrix? | |
| Jan 27, 2021 at 15:32 | comment | added | Carl Witthoft | @GerryMyerson that would be yet another variation in the puzzle :-) . For my current form, I'd need 2^5*9^2 to map to , e.g. 222223333 or 232323232 | |
| Jan 26, 2021 at 22:33 | comment | added | Gerry Myerson | Are you interested in $2^59^2=2592$? | |
| Jan 26, 2021 at 21:11 | comment | added | Carl Witthoft | @user44191 sorry, I should have emphasized the composite number part of the conjectures | |
| Jan 26, 2021 at 19:15 | comment | added | user44191 | Any prime number where $1$ appears as a digit exactly once will work. | |
| Jan 26, 2021 at 13:02 | review | Close votes | |||
| Jan 30, 2021 at 8:05 | |||||
| Jan 26, 2021 at 12:48 | review | First posts | |||
| Jan 26, 2021 at 13:42 | |||||
| Jan 26, 2021 at 12:43 | history | asked | Carl Witthoft | CC BY-SA 4.0 |