Data commit

Task/Attractive-numbers/Prolog/attractive-numbers.pro

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+prime_factors(N, Factors):-
+    S is sqrt(N),
+    prime_factors(N, Factors, S, 2).
+
+prime_factors(1, [], _, _):-!.
+prime_factors(N, [P|Factors], S, P):-
+    P =< S,
+    0 is N mod P,
+    !,
+    M is N // P,
+    prime_factors(M, Factors, S, P).
+prime_factors(N, Factors, S, P):-
+    Q is P + 1,
+    Q =< S,
+    !,
+    prime_factors(N, Factors, S, Q).
+prime_factors(N, [N], _, _).
+
+is_prime(2):-!.
+is_prime(N):-
+    0 is N mod 2,
+    !,
+    fail.
+is_prime(N):-
+    N > 2,
+    S is sqrt(N),
+    \+is_composite(N, S, 3).
+
+is_composite(N, S, P):-
+    P =< S,
+    0 is N mod P,
+    !.
+is_composite(N, S, P):-
+    Q is P + 2,
+    Q =< S,
+    is_composite(N, S, Q).
+
+attractive_number(N):-
+    prime_factors(N, Factors),
+    length(Factors, Len),
+    is_prime(Len).
+
+print_attractive_numbers(From, To, _):-
+    From > To,
+    !.
+print_attractive_numbers(From, To, C):-
+    (attractive_number(From) ->
+        writef('%4r', [From]),
+        (0 is C mod 20 -> nl ; true),
+        C1 is C + 1
+        ;
+        C1 = C
+    ),
+    Next is From + 1,
+    print_attractive_numbers(Next, To, C1).
+
+main:-
+    print_attractive_numbers(1, 120, 1).