Suppose that a positive integer N can be expressed as the sum of k consecutive positive integers N = a + (a + 1) + (a + 2) + · · · + (a + k − 1)
for k = 2017 but for no other values of k > 1.

Considering all positive integers N with this property, what is the smallest positive integer a that occurs in any of these expressions?

Source: Putnam 2017