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Old 2020-10-11, 18:10   #1
R2357
 
"Ruben"
Oct 2020
Nederland

2×19 Posts
Smile 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 :)
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Old 2020-10-11, 18:37   #2
Viliam Furik
 
Jul 2018
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OEIS sequence A217040? Bases b in which the increasing concatenation of all primes smaller than b forms a prime number.
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Old 2020-10-11, 18:55   #3
R2357
 
"Ruben"
Oct 2020
Nederland

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Well done!
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Old 2020-10-11, 19:37   #4
Viliam Furik
 
Jul 2018
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Quote:
Originally Posted by R2357 View Post
Well done!
Well, that was quick... Another one, please!
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Old 2020-10-11, 20:22   #5
Uncwilly
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Aug 2003
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3, 4, 9, 8, 9, 9, 8, 9, 9, 8...

Last fiddled with by Uncwilly on 2020-10-11 at 21:50
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Old 2020-10-11, 20:25   #6
sweety439
 
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Nov 2016

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Quote:
Originally Posted by R2357 View Post
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)
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Old 2020-10-11, 20:43   #7
Viliam Furik
 
Jul 2018
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Quote:
Originally Posted by Uncwilly View Post
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.
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Old 2020-10-11, 21:49   #8
Uncwilly
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Quote:
Originally Posted by Viliam Furik View Post
I will gues OEIS A239384
That sequence starts with 1. I made an error. I have now corrected the sequence.
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Old 2020-10-11, 23:32   #9
a1call
 
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"Rashid Naimi"
Oct 2015
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oeis won't help you for this one:


4, 11,14, 17
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Old 2020-10-12, 00:41   #10
a1call
 
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"Rashid Naimi"
Oct 2015
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Quote:
Originally Posted by a1call View Post
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.
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Old 2020-10-12, 05:58   #11
R2357
 
"Ruben"
Oct 2020
Nederland

2×19 Posts
Smile Another riddle :)

Quote:
Originally Posted by Viliam Furik View Post
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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