Express 169 as the sum of first 13 odd numbers.

We have   169 = 13² 

               = Sum of first odd numbers
               = 1 + 3 + 5 + 7 + 9 + 11 + 13 + 15 + 17 + 19 + 21 + 23 + 25
               = (1 + 25) + (3 + 23) + (5 + 21) + (7+ 19) + (9 + 17) + (11 + 15) +13
               = 26 + 26 + 26 + 26 +26 + 26 + 13
               =  (6 x 26) + 13 = 156 + 13 = 169