Write a function, triangle_number_recursion(num), which returns the sum 1 + 2 + 3...+ n. Triangle numbers are calculated by summing up all the values from 1 ton. Back in Algebra class, n(n+1) you probably learned that you could calculate that sum, quite easily, with the formula (write a function that calculates it recursively FOR LOOPS/WHILE LOOPS NOT ALLOWED) 2