Quiz 66: Find if number is special number

Problem:

Given a number N. N is considered special if for any positive integer i, N=(i*(i+1))/2. Print "YES" if N is special number, else print "NO"

Input Format: 

N

Output Format: 

YES/NO

Constraints: 

None

Sample Input

210

Sample Output:

YES

Explanations:

for i=20,(20*21)/2=210. So 210 is special number

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Solution:

chomp($n=<STDIN>);
$c=sqrt((8*$n)+1);
if($c == int($c))
{
print "YES";
}
else
{
print "NO";
}

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Tips:

Solving maths equation, you can narrow down to check if 8N+1 is a perfect square.