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 2020-10-11, 18:10 #1 R2357   "Ruben" Oct 2020 Nederland 3810 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 :)
 2020-10-11, 18:37 #2 Viliam Furik   "Viliam Furík" Jul 2018 Martin, Slovakia 3×151 Posts OEIS sequence A217040? Bases b in which the increasing concatenation of all primes smaller than b forms a prime number.
 2020-10-11, 18:55 #3 R2357   "Ruben" Oct 2020 Nederland 2×19 Posts Well done!
2020-10-11, 19:37   #4
Viliam Furik

"Viliam Furík"
Jul 2018
Martin, Slovakia

3×151 Posts

Quote:
 Originally Posted by R2357 Well done!
Well, that was quick... Another one, please!

 2020-10-11, 20:22 #5 Uncwilly 6809 > 6502     """"""""""""""""""" Aug 2003 101×103 Posts 100101010011002 Posts 3, 4, 9, 8, 9, 9, 8, 9, 9, 8... Last fiddled with by Uncwilly on 2020-10-11 at 21:50
2020-10-11, 20:25   #6
sweety439

Nov 2016

2,819 Posts

Quote:
 Originally Posted by R2357 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 :)
They are all divisors of 360 (the number of degrees in a turn)

2020-10-11, 20:43   #7
Viliam Furik

"Viliam Furík"
Jul 2018
Martin, Slovakia

3·151 Posts

Quote:
 Originally Posted by Uncwilly 3, 4, 9, 8, 9, 8...
I will gues OEIS A239384 - (Decimal expansion of the probability of a normal-error variable exceeding the mean by more than three standard deviations), however it's most probably not correct, since you now know I search in OEIS.

2020-10-11, 21:49   #8
Uncwilly
6809 > 6502

"""""""""""""""""""
Aug 2003
101×103 Posts

954810 Posts

Quote:
 Originally Posted by Viliam Furik I will gues OEIS A239384
That sequence starts with 1. I made an error. I have now corrected the sequence.

 2020-10-11, 23:32 #9 a1call     "Rashid Naimi" Oct 2015 Remote to Here/There 2,017 Posts oeis won't help you for this one: 4, 11,14, 17
2020-10-12, 00:41   #10
a1call

"Rashid Naimi"
Oct 2015
Remote to Here/There

2,017 Posts

Quote:
 Originally Posted by a1call oeis won't help you for this one: 4, 11,14, 17
Hint: They are all consecutive integers n for which f1(n) and f2(n) are Twin-Prime-Pairs.

2020-10-12, 05:58   #11
R2357

"Ruben"
Oct 2020
Nederland

2616 Posts
Another riddle :)

Quote:
 Originally Posted by Viliam Furik Well, that was quick... Another one, please!

Here goes, what do pi and the prime number sequence have in common (apart from pi's usage in the prime counting function and in the Gapcoin symbol)?

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