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Project Euler - Problem 3

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  1. largest_prime_factor(Number, Prime) :-
  2. 	N is round(sqrt(Number)),
  3. 	largest_prime_factor(Number, N, Prime).
  4.  
  5. largest_prime_factor(Number, N, N) :-
  6. 	divisible(Number, N),
  7. 	prime(N), !.
  8. largest_prime_factor(Number, N, Prime) :-
  9. 	Next is N-1,
  10. 	largest_prime_factor(Number, Next, Prime).
  11.  
  12.  
  13.  
  14. divisible(Number, 0) :-
  15. 	write('Error: division by 0').		
  16. divisible(Number, Divisor) :-
  17. 	Number mod Divisor =:= 0.
  18.  
  19.  
  20.  
  21. prime(Number) :-
  22. 	N is round(sqrt(Number)),
  23. 	prime(Number, 1, N).
  24.  
  25. prime(Number, N, N) :-	!.	
  26. prime(Number, Divisor, End) :-
  27. 	Divisor < End,
  28. 	NextDivisor is Divisor + 1,
  29. 	\+ divisible(Number, NextDivisor),
  30. 	prime(Number, NextDivisor, End).

URL: http://13tazer31.wordpress.com/2011/02/06/project-euler-problem-3/

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