diff --git a/Number Theory/prime_sieve.cpp b/Number Theory/prime_sieve.cpp
new file mode 100644
index 0000000..3b08be4
--- /dev/null
+++ b/Number Theory/prime_sieve.cpp	
@@ -0,0 +1,18 @@
+#define MAX_N 5000001
+bool is_prime[MAX_N];
+
+bool is_sieve_eval = false;
+
+void sieve_erathosis(){
+	if( is_sieve_eval ) return;
+	is_sieve_eval = true;
+	memset(is_prime,0,sizeof(is_prime));
+	is_prime[0] = true , is_prime[1] = true;
+	for(int num = 2 ; num*num < MAX_N ; num++ ){
+		if( !is_prime[num] ){
+			for(int val = num*num ; val < MAX_N ; val += num ){
+				is_prime[val] = true;
+			}
+		}
+	}
+}
\ No newline at end of file