;Definition
A '''Giuga number''' is a composite number '''n''' which is such that each of its distinct prime factors
'''f''' divide (n/f - 1) exactly.

All known Giuga numbers are even though it is not known for certain that there are no odd examples. 

;Example
30 is a Giuga number because its distinct prime factors are 2, 3 and 5 and:
* 30/2 - 1 = 14 is divisible by 2
* 30/3 - 1 = 9 is divisible by 3
* 30/5 - 1 = 5 is divisible by 5
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;Task
Determine and show here the first four Giuga numbers.

;Stretch
Determine the fifth Giuga number and any more you have the patience for.

;References

* [[wp:Giuga_number|Wikipedia: Giuga number]]
* [[oeis:A007850|OEIS:A007850 - Giuga numbers]]
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