It is divisible by 3 but not divisible by 9.
To test for divisibility by 3, sum the digits and if the sum is divisible by 3 then so is the original number; the test can be repeated ion the sum, so keep summing until a single digit remains and if this single digit is 3, 6 or 9, then the original number is divisible by 3:
5673 → 5 + 6 + 7 + 3 = 21 → 2 + 1 = 3 which is one of {3, 6, 9} so 5673 is divisible by 3.
To test for divisibility by 9, sum the digits and if the sum is divisible by 9 then so is the original number; the test can be repeated ion the sum, so keep summing until a single digit remains(this single digit is known as the digital root of the number) and if this single digit is 9, then the original number is divisible by 9:
5673 → 5 + 6 + 7 + 3 = 21 → 2 + 1 = 3 which is not 9 so 5673 is not divisible by 9.
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3 or 9
If a number is not divisible by 3 then it is not divisible by 9.
It is impossible since 3 can already go into 9.
To check for divisibility by 9 sum the digits of the number and if this sum is divisible by 9 then so is the original number. For 32643: 3 + 2 + 6 + 4 + 3 = 18 which is divisible by 9 so 32643 is divisible by 9. As 9 = 3 × 3, any number divisible by 9 is also divisible by 3, thus as 32643 is divisible by 9 it is also divisible by 3. However, for completeness: to check for divisibility by 3 sum the digits of the number and if this sum is divisible by 3 then so is the original number. For 32643: 3 + 2 + 6 + 4 + 3 = 18 which is divisible by 3 so 32643 is divisible by 3.
Any that are divisible by 9 are also divisible by 3.