
FRACTRAN - the esoteric programming language invented by John H Conway - robinhouston
http://en.wikipedia.org/wiki/FRACTRAN
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dalke
That was neat. Here's an implementation in Python:

    
    
        # Python implementation of Conway's prime formula for FRACTRAN
        # The output is the sequence A034785.
        
        from fractions import Fraction as F
        
        terms = [F(17, 91), F(78, 85), F(19, 51), F(23, 38), F(29, 33),
                 F(77, 29), F(95, 23), F(77, 19), F(1, 17), F(11, 13),
                 F(13, 11), F(15, 14), F(15, 2), F(55, 1)]
        
        n = 2
        print n
        
        while 1:
            for i, f in enumerate(terms):
                fn = f * n
                if fn.denominator == 1:
                    n = fn.numerator
                    print n
                    break
            else:
                break

