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sorting out a problem


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#1 phil1882

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Posted 06 March 2014 - 02:29 AM

currently i'm studying the sequence

1 2 3 5 7 8 11 12 13 17 19 20 23 27 28 29 30 31....

which is the odd product of prime numbers.

i'm curious to know if there is a good counting function for the number of them below say 10,000,000.

if so, can it be reversed to find approximately the nth odd product?

 


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#2 Perhaps check it again

Perhaps check it again

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Posted 06 March 2014 - 06:47 AM

phil1882,

 

1) The sequence starts off with "2," not "1," because 1 is not a prime number.

 

2) There are commas between the numbers in the sequence and a comma before the ellipsis.

 

3) You are missing the number 18.  18 = 2*3*3  (The number of prime factors is odd.)

 

 

Therefore, the sequence is:

 

2, 3, 5, 7, 8, 11, 12, 13, 17, 18, 19, 20, 23, 27, 28, 29, 30, 31, ...


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#3 plasmid

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Posted 06 March 2014 - 07:39 AM

Spoiler for initial guess

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