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Seven given - the eighth TBD (Posted on 2018-03-14) Difficulty: 4 of 5
3, 23, 17, 5, 7, 67, 39, X.

The above line represents a finite sequence of 8 integers.

7 are spelled out, the last one is left to be added by you.


If asked to continue the sequence, what options do you suggest
for the next 3 members?

There are several valid solutions.

See The Solution Submitted by Ady TZIDON    
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Comments: ( Back to comment list | You must be logged in to post comments.)
Some Thoughts re(2): a possible one | Comment 3 of 6 |
(In reply to re: a possible one by Ady TZIDON)

It is clear that all the numbers are primes except 39. This is quite weird. So I decided to put the sequence of prime numbers in a sequence database. This numbers match the eleven row of the sequence of the highest prime divisors of k*n+1. In our case n=11


The sequence k*11+1 goes
12,23,34,45,56,67,78,89
and the correlative sequence of the highest prime divisors is
3,23,17,5,7,67,13,89

Ths would solved the puzzle except that instead of 13 we have a 39 in the seven term. 39=13*3 so here the higher prime has probably been replaced by the product of the two highest primes of 78 (13,3,2; 13*3=39) 

If we follow the sequence introducing that change (product instead of just the highest) in the next terms we get
89 (89,1)
25 from 100 =5^2*2^2 => (5,5)
111 from 111=37*3 =>(37,3)
122 from 122=61*2 =>(61,2)

Edited on March 14, 2018, 5:08 pm
  Posted by armando on 2018-03-14 16:45:38

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