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Forum: And now for something completely different 2021-09-23, 00:29
Replies: 13
Views: 815
Posted By Batalov
That is funny (if it was supposed to be a joke) -...

That is funny (if it was supposed to be a joke) - but incorrect.
9-digit palindrome primes exist and there are tons of them. For example, 100030001.
1234567...
Forum: And now for something completely different 2021-09-21, 19:53
Replies: 13
Views: 815
Posted By Batalov
Credit (and SIM-) card numbers have the similar...

Credit (and SIM-) card numbers have the similar (not the same (https://en.wikipedia.org/wiki/Luhn_algorithm)) protection from typos and transpositions.
Forum: And now for something completely different 2021-09-21, 19:31
Replies: 13
Views: 815
Posted By Batalov
Lightbulb I've actually been asked, so I could repost here...

I've actually been asked, so I could repost here exactly why every "even-length" palindrome is divisible by "11" (think decimal, but it is true for any base b).
We could simply say that order of...
Forum: And now for something completely different 2021-09-17, 17:49
Replies: 13
Views: 815
Posted By Batalov
...but 10^(n)-epsilon has n digits And of...

...but 10^(n)-epsilon has n digits

And of course, the only palindrome prime that has an even number of digits (in any base, actually) is "11"! (And even "11" can be composite; then none.)
All...
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