20201011, 18:10  #1 
"Ruben"
Oct 2020
Nederland
2×19 Posts 
A little puzzle
Hello,
I thought I would give the forum a little puzzle that I made :) Here is the puzzle : What do the numbers 3, 4, 5, 9, 10 and 15 have in common? Have fun solving :) 
20201011, 18:37  #2 
"Viliam Furík"
Jul 2018
Martin, Slovakia
13×29 Posts 
OEIS sequence A217040? Bases b in which the increasing concatenation of all primes smaller than b forms a prime number.

20201011, 18:55  #3 
"Ruben"
Oct 2020
Nederland
2·19 Posts 
Well done!

20201011, 19:37  #4 
"Viliam Furík"
Jul 2018
Martin, Slovakia
13·29 Posts 

20201011, 20:22  #5 
6809 > 6502
"""""""""""""""""""
Aug 2003
101×103 Posts
9352_{10} Posts 
3, 4, 9, 8, 9, 9, 8, 9, 9, 8...
Last fiddled with by Uncwilly on 20201011 at 21:50 
20201011, 20:25  #6 
Nov 2016
2820_{10} Posts 

20201011, 20:43  #7 
"Viliam Furík"
Jul 2018
Martin, Slovakia
179_{16} Posts 

20201011, 21:49  #8 
6809 > 6502
"""""""""""""""""""
Aug 2003
101×103 Posts
2^{3}·7·167 Posts 

20201011, 23:32  #9 
"Rashid Naimi"
Oct 2015
Remote to Here/There
2^{6}×31 Posts 
oeis won't help you for this one:
4, 11,14, 17 
20201012, 00:41  #10 
"Rashid Naimi"
Oct 2015
Remote to Here/There
2^{6}×31 Posts 

20201012, 05:58  #11 
"Ruben"
Oct 2020
Nederland
38_{10} Posts 
Another riddle :)

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