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This question is about "Which number is prime number". Let us see defination of "Prime Number" again
What is a prime number?
A number is greater than 1 is called a prime number, if it has only two factors, 1 and the number itself i.e 2, 3, 5, 7, 11 ... also notice that prime number are start form 2.
1 has only one positive divisor that is itself. therefore 1 is not a prime number.
39 has following positive divisor.
1, 3, 13 and 39. we have check this divisible by 3 math shortcut trick.
49 has following positive divisor.
1, 7, 49. It is very simple that 49 is divisble by 7. we can also check it by divisible by 7 math shortcut trick.
Therefore 1, 7, 49 are not prime number. None of above is prime number.