diff --git a/solutions/sol18.py b/solutions/sol18.py
new file mode 100644
index 0000000..0830897
--- /dev/null
+++ b/solutions/sol18.py
@@ -0,0 +1,17 @@
+#Himanshu Nachane (@Himanshu1495)
+'''return missing number in an input array of consecutively increasing numbers.
+
+i: [5,6,8,9]
+o: 7
+'''
+
+def missing_num(arr):
+	first_element = arr[0]
+	last_element = arr[-1]
+	new_sum = 0
+	for x in range(first_element,last_element+1):
+		new_sum += x
+	return new_sum - sum(arr)
+
+
+
diff --git a/test/18.py b/test/18.py
new file mode 100644
index 0000000..164ffa9
--- /dev/null
+++ b/test/18.py
@@ -0,0 +1,14 @@
+import sys
+sys.path.insert(0,'../solutions/')
+from sol18 import missing_num
+import unittest
+
+class MyTest(unittest.TestCase):
+    def test1(self):
+        self.assertEqual(missing_num([10,11,12,14,15,16]),13)
+    def test2(self):
+        self.assertEqual(missing_num([125,126,128,129,130]),127)
+    def test3(self):    
+        self.assertEqual(missing_num([1125,1127,1128,1129,1130]),1126)
+
+unittest.main()