It is possible to find out using mathematical methods whether a given integer is a prime number or not.
Yes, 18 241 439 is a prime number.
Indeed, the definition of a prime numbers is to have exactly two distinct positive divisors, 1 and itself. A number is a divisor of another number when the remainder of Euclid’s division of the second one by the first one is zero. Concerning the number 18 241 439, the only two divisors are 1 and 18 241 439. Therefore 18 241 439 is a prime number.
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Since 18241439 is a prime number, 18241439 is also a deficient number, that is to say 18241439 is a natural integer that is strictly larger than the sum of its proper divisors, i.e., the divisors of 18241439 without 18241439 itself (that is 1, by definition!).