answer:Let i originally equal 1. n ∑ ab+a+b = 719 //719 for this problem, anyway. i = 1 Where a ≠ b, 1 ≤ a ≤ 5, 1 ≤ b ≤ 5, and b comes one term after a in the sequence. //Technically, order doesn’t matter, but it makes the ∑ make sense. ab+a+b = z Replace a and b with the new number z in the sequence and continue the summation. i = z So, after the first iteration, the equation becomes: n ∑ ab+a+b = 719 i = z 1 2 3 4 5 (1*2+1+2) = 5 5 3 4 5 5*3+5+3 = 23 23 4 5 23*4+23+4 = 119 119 5 119*5+119+5 = 719 I would have to pull out my Discrete Mathematics notebook to come up with a simple formula. I’ll come back to this question when I have time. If you’re into Computer Science, think of it as a “for loop.” As far as why order doesn’t matter, that’s kind of a trick question. The order of operations matters, so that’s why the order of the numbers from a group that you act upon doesn’t; sort of like Commutative Laws, eventually, you would get the same result no matter what two numbers you multiply and add up first in a list.