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Ingy döt Net 2013-04-10 23:57:08 -07:00
commit b83f433714
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Task/Primality-by-trial-division/Prolog/primality-by-trial-division.pro Normal file
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prime(2).
prime(N) :- integer(N), N > 1,
M is floor(sqrt(N+1)), % round-off paranoia
N mod 2 > 0, % is odd
check_by_odds(N, M, 3).
check_by_odds(N, M, S) :-
M2 is (M-1) // 2, S2 is S // 2,
forall( between(S2,M2,X), N mod (2*X+1) > 0 ).
/*
check_by_odds(N, M, F) :- F > M.
check_by_odds(N, M, F) :- F =< M,
N mod F > 0,
F1 is F + 2, % test by odds only
check_by_odds(N, M, F1).*/