Atriangular number is a number that is the sum of the integers from 1 to some integer n. thus 1 is a triangular number because it's the sum of the integers from 1 to 1; 6 is a triangular number because it's 1+2+3=6. given the non-negative integers m and n (with m < n), create a list of the triangular numbers between (and including) m and n. thus if m is 3 and n is 20, the list would be: [3, 6