The correct answer is (D):
Given, (n – 1) (n) (n + 1) = 15600
As 15600 has 2 zeroes in it, one of n – 1, n or n + 1 should be a multiple of 25.
Dividing 15600 by 25, we get 624, but 624 = 24*26 so, the numbers are 24, 25 and 26
242 + 252 + 262 = 1877