Giuga numbers: Difference between revisions

=={{header|ALGOL W}}==

{{Trans|ALGOL 68}}

<syntaxhighlight lang="algolw">

begin % find some Giuga numbers, composites n such that all their distinct %

% prime factors f exactly divide ( n / f ) - 1 %

% find the first four Giuga numbers %

% each prime factor must appear only once, e.g.: for 2: %

% [ ( n / 2 ) - 1 ] mod 2 = 0 => n / 2 is odd => n isn't divisible by 4 %

% similarly for other primes %

integer gCount, n;

gCount := 0;

n := -2;

while begin n := n + 4;

gCount < 4

end

do begin % assume the numbers are all even %

integer v, f, fCount;

logical isGiuga;

v := n div 2;

isGiuga := TRUE;

fCount := 1;

f := 1;

while begin f := f + 2;

f <= v and isGiuga

end

do begin

if v rem f = 0 then begin

% have a prime factor %

fCount := fCount + 1;

isGiuga := ( ( n div f ) - 1 ) rem f = 0;

v := v div f

end if_v_rem_f_eq_0

end while_f_le_v_and_isGiuga ;

if isGiuga then begin

% n is still a candidate, check it is not prime %

if fCount > 1 then begin

gCount := gCount + 1;

writeon( i_w := 1, s_w := 0, " ", n )

end if_fCount_gt_1

end if_isGiuga

end while_gCount_lt_4

end.

</syntaxhighlight>

{{out}}

Same as Algol 68