using System;
using System.Collections.Generic;
class PrimeConcat
{
// Function to check primality
static bool IsPrime(long n) {
if (n < 2) return false;
if (n % 2 == 0 && n != 2) return false;
for (long i = 3; i * i <= n; i += 2) {
if (n % i == 0) return false;
}
return true;
}
// Concatenate two integers
static long Concat(int a, int b) {
string s = a.ToString() + b.ToString();
return long.Parse(s);
}
static void Main()
{
int limit = 12; // you can increase this
List<int> primes = new List<int>();
// Generate primes up to limit
for (int i = 2; i <= limit; i++) {
if (IsPrime(i)) {
primes.Add(i);
}
}
// Check pairs
for (int i = 0; i < primes.Count; i++) {
for (int j = 0; j < primes.Count; j++) {
if (i == j) continue; // skip same prime if you want
long num = Concat(primes[i], primes[j]);
if (IsPrime(num)) {
Console.WriteLine($"{primes[i]} + {primes[j]} -> {num} is prime");
}
}
}
}
}
/*
run:
2 + 3 -> 23 is prime
2 + 11 -> 211 is prime
3 + 7 -> 37 is prime
3 + 11 -> 311 is prime
5 + 3 -> 53 is prime
7 + 3 -> 73 is prime
11 + 3 -> 113 is prime
*/
