

A circular sieve of eratosthenes to visualize prime numbers - nobody_nowhere
http://www.sievesofchaos.com/

======
3pt14159
After reading this awesome article I decided to write my own version of
exactly what I saw in his pictures:

timing_array = Hash.new

for q in 0..6

    
    
      max_n = 10**q
    
      prime_array = Array.new
    
      for z in 0..max_n
    
        prime_array[z] = 0
    
      end
    
      for i in 2..max_n
    
        a = max_n / i
    
        for j in 1..a
    
          prime_array[j*i] += 1 unless j*i > max_n
    
        end
    
      end
    
      puts "prime numbers to #{max_n}"
    
      prime_array.each_with_index {|num,v| puts "#{v}" unless num > 1}
    
      timing_array[max_n] = Time.now
    

end

puts "and the resultz"

puts timing_array

1000000 Sun Dec 13 20:33:05 -0500 2009

100000 Sun Dec 13 20:32:34 -0500 2009

10000 Sun Dec 13 20:32:31 -0500 2009

1000 Sun Dec 13 20:32:31 -0500 2009

100 Sun Dec 13 20:32:31 -0500 2009

------
zandorg
I had a kind of program which would find primes higher than the Sieve of
Eratosthenes (typically this only goes up to 4 billion because of 1 bit per
integer), called a 'Leapfrog' sieve, but someone said it wasn't very
interesting, and I can't tell if it's been done before.

~~~
pronoiac
Prime Links - <http://primes.utm.edu/links/programs/> \- doesn't have anything
about Leapfrog.

On Ubuntu, if you install bsdgames, "primes" can generate a list of primes up
to (checks) 2^32 (4.29 billion & change).

djb's primegen - <http://cr.yp.to/primegen.html> \- goes up to
1000000000000000 (10^15).

------
Asa-Nisse
Someone should tell this guy about google docs..

~~~
naz
And the GIF file format

