It would probably refer to a digit that is a Prime number, or a composite number. Note that mathematicians normally talk about prime and composite NUMBERS, not individual digits.
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It is composite, as are all whole numbers whose last digits are even.
102
Nope it's Composite because the sum of digits is divisible by 3.
No because as for example 23 is a prime number but 32 is a composite number
23, 29 and 31 are prime. The rest are composite.