# Python Program to Check Triangular Number

#### This Python program checks whether a given number by user is Triangular number or not.

Triangular Numbers are those numbers which are obtained by continued summation of the natural numbers 1, 2, 3, 4, 5, ...

Triangular Number Example: 15 is Triangular Number because it can be obtained by 1+2+3+4+5+6 i.e. 1+2+3+4+5+6=15

List of Triangular Numbers: 1, 3, 6, 10, 15, 21, 28, 36, 45, 55, 66, 78, 91, 105, 120, 136, 153, 171, 190, 210, 231, 253, 276, 300, 325, 351, 378, 406, 435, 465, 496, 528, 561, 595, 630, 666,

## Python Source Code: Triangular Number Check

``````
# Python program to check Triangular Number

# Function to check Triangular

def is_triangular(n):

if n==0 or n==1:
return True

triangular_sum = 0

for i in range(n):
triangular_sum += i

if triangular_sum == n:
return True

if i == n:
return False

number = int(input('Enter number: '))

# Making decision
if is_triangular(number):
print('%d is TRIANGULAR.' %(number))
else:
print('%d is NOT TRIANGULAR.' %(number))
``````

## Triangular Number Check Python Output

```Run 1:
-----------------
Enter number: 15
15 is TRIANGULAR.

Run 2:
-----------------
Enter number: 696
696 is NOT TRIANGULAR.
```