It is possible to find out using mathematical methods whether a given integer is a prime number or not.
Yes, 494 541 259 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 494 541 259, the only two divisors are 1 and 494 541 259. Therefore 494 541 259 is a prime number.
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Since 494541259 is a prime number, 494541259 is also a deficient number, that is to say 494541259 is a natural integer that is strictly larger than the sum of its proper divisors, i.e., the divisors of 494541259 without 494541259 itself (that is 1, by definition!).