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2021-09-15, 11:19   #265
paulunderwood

Sep 2002
Database er0rr

5×7×109 Posts

Quote:
 Originally Posted by sweety439 https://primes.utm.edu/primes/status.php id 132704 and 132705 are palindromes.
No they are not Reversing the digits does not give the same number.

https://primes.utm.edu/primes/page.php?id=132715 is a palindrome. Congrats Serge and Ryan.

UTM's Prime Pages parser calculated the decimal digits as 1234568

Last fiddled with by paulunderwood on 2021-09-15 at 11:45

2021-09-15, 16:06   #266
Batalov

"Serge"
Mar 2008
Phi(4,2^7658614+1)/2

26×149 Posts

Quote:
 Originally Posted by paulunderwood UTM's Prime Pages parser calculated the decimal digits as 1234568
Prof.Caldwell's calculator had insufficient precision. I'll drop him a note. It is, of course, 1234567.

All palindromes of even length (except 11) are composite!
Hint: they are divisible by 11

2021-09-15, 18:17   #267
rudy235

Jun 2015
Vallejo, CA/.

17558 Posts

Quote:
 Originally Posted by paulunderwood I am looking forward to its revelation. The largest palindrome before this one had 490,001 digits. So 1,234,567 digits is quite amazing considering its crunching is done with generic modular reduction.
Wow! A megaprime palindrome. And one with more than twice the digits than the previous one!

I have to see it to believe it!

 2021-09-15, 21:52 #268 Batalov     "Serge" Mar 2008 Phi(4,2^7658614+1)/2 254016 Posts When I was already way into sieving, I thought that I should have picked 1234321 decimal digits length But it turned out good. With 1234567 digits' dataset the hit came, statistically speaking, very! early. So it was lucky.
 2021-09-21, 00:39 #269 paulunderwood     Sep 2002 Database er0rr 5·7·109 Posts The prof has been busy. He fixed the palindrome length and puzzle-peter's arithmetic progression, which comes second on table two of https://primes.utm.edu/top20/page.php?id=14. Hint: An AP9 could be quite easy to find to make it to the top of table two. For the AP8, I wrote my own GWNUM code which was 15% faster, I think mainly by dropping repetitive evaluations of the primorial coefficient. I'd willing to share it with any interested parties. Last fiddled with by paulunderwood on 2021-09-21 at 00:41
 2021-09-21, 01:30 #270 Batalov     "Serge" Mar 2008 Phi(4,2^7658614+1)/2 100101010000002 Posts Good! Excellent! Even Kamada-san wrote to him and cc:'d me (as if I could help ). But it is fixed now, cool beans.
2021-09-22, 10:07   #271
pepi37

Dec 2011
After milion nines:)

146810 Posts

Quote:
 Originally Posted by Batalov When I was already way into sieving, I thought that I should have picked 1234321 decimal digits length But it turned out good. With 1234567 digits' dataset the hit came, statistically speaking, very! early. So it was lucky.

So if it is not secret how many candidates was tested before prime appear?

2021-09-22, 12:51   #272
ryanp

Jun 2012
Boulder, CO

313 Posts

Quote:
 Originally Posted by pepi37 So if it is not secret how many candidates was tested before prime appear?
About 18,000 of the ~316K inputs that Serge originally sent me.

P.S. (S.B.) - the exact row number for the hit was 13,239th

2021-09-22, 20:54   #273
pepi37

Dec 2011
After milion nines:)

22×367 Posts

Quote:
 Originally Posted by ryanp About 18,000 of the ~316K inputs that Serge originally sent me. P.S. (S.B.) - the exact row number for the hit was 13,239th

13239-th: small number of candidates for such prime. Very lucky hit :)

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