# Find a Missing Number From a Sequence of Consecutive Numbers

**Objective :** You have been asked to Write an algorithm Find a Missing Number From a Sequence of Consecutive Numbers

**Input:** Array, arrA[] with a missing number and Range

**Output : **missing number

**Approach:**

- Approach is very simple, Add all the given numbers say S
- Calculate sum of N numbers by formula n(n+1)/2 , say N
- Find missing number m = N-S

**Example :** suppose array given is {1,2,3,4,5,6,8,9,10} and range is 10.

So N will be sum of 1 to 10 = 10(10+1)/2 = 55

S will be sum of all the array elements which is = 48

So missing number will be = 55-48 = 7

**Complete Code:**

**Output :**

Missing number is :6