add: sieve_of_eratosthenes.py

Math/sieve_of_eratosthenes.py

@@ -0,0 +1,30 @@
+"""Sieve Of Eratosthenes:
+The sieve of eratosthenes is one of the most efficient way to find all
+the prime numbers upto the number `n`
+
+for more reference(https://www.geeksforgeeks.org/sieve-of-eratosthenes/)
+"""
+
+#importing `math` module which will be used later
+import math
+
+#specify upto where you have to find the prime numbers
+n = int(input("Enter the range : ")) 
+
+#`arr` is a boolean list that contains `n+1` `False` entries
+arr = [False]*(n+1)
+
+#loop upto the square root of the range `n`
+for i in range(2,int(math.sqrt(n))+1):
+    if arr[i] == False:
+        for j in range(i*i, n+1, i):
+            #making the entry `True` for all entries whose index is the multiple
+            arr[j] = True
+
+#after the loop exits, all the entry that are prime numbers
+#are marked as `False`
+
+#printing all the prime numbers
+for i in range(2,n):
+    if arr[i+1] == False:
+        print(i+1)