Giuga numbers: Difference between revisions
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=={{header|ABC}}==
Based on the Algol 68 sample,
<syntaxhighlight lang="abc">
HOW TO REPORT is.giuga n:
\ 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
PUT 1, 3, 1, floor( n / 2 ) IN f.count, f, giuga, v
WHILE f <= v AND giuga = 1:
IF v mod f = 0:
PUT f.count + 1 IN f.count
IF ( ( floor( n / f ) ) - 1 ) mod f <> 0: PUT 0 IN giuga
PUT floor( v / f ) IN v
PUT f + 2 IN f
IF giuga = 1: \ n is still a candidate, check it is not prime
IF f.count = 1: FAIL \ only 1 factor - it is prime so not giuga
REPORT giuga = 1
PUT 0, -2 IN g.count, n
WHILE g.count < 4:
PUT n + 4 IN n \ assume the numbers are all even
IF is.giuga n:
PUT g.count + 1 IN g.count
WRITE n
</syntaxhighlight>
{{out}}
<pre>
30 858 1722 66198
</pre>
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