Problem #1892 on PBinfo
With the given number n, find out if the number is lucky or not We call the number n lucky if and only if it's square (n*n) can be written as a sum of n consecutive numbers.
Examples : 3 it's lucky because 3 _ 3 = 2 + 3 + 4 7 it's lucky because 7 _ 7 = 4 + 5 + 6 + 7 + 8 + 9 + 10