>>>I need to create algorithm (based on an integer number) that by applying some formula or equation to this number I can identify if the number belongs to group 1, 2, or 3 or any combination of them (e.g. 1 and 2, 1 and 3, 1 and 2 and 3, 2 and 3)
>>>For example, number 8 would indicate belonging to all three groups (since I can divide this number by the group number without a remainder.
>>>Any suggestions?
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>>Either I'm horribly misunderstanding you, or my math is worse than I thought. How do you divide 8 by 3 and leave no remainder?
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>If you round up to the nearest multiple of 3, then divide, you'll have no remainder. (Of course... that'll also mean that all numbers you choose will automatically belong to group 3)

Besides, it would be cheating. ;)