include

int isPrime(int n, int i) {
if (n <= 2) {
return (n == 2) ? 1 : 0;
}

if (n % i == 0) {
return 0;
}
if (i * i > n) {
return 1;
}
return isPrime(n, i + 1);

}

int main() {
int n;

printf("Enter a natural number: ");
scanf("%d", &n);
if (isPrime(n, 2)) {
printf("%d is a prime number.\n", n);
} else {
printf("%d is not a prime number.\n", n);
}
return 0;

}

/* Пример работы программы:
Enter a natural number: 17
17 is a prime number.

Enter a natural number: 24
24 is not a prime number. */