Using repeated subtraction of consecutive odd numbers from 1, after how many steps will you reach 0 starting from 121?

121 = 11², and the sum of the first n odd numbers equals n². So repeated subtraction of the odd numbers 1, 3, 5, …, 21 from 121 — that's 11 odd numbers — brings the total down to 0. This is also how you can test whether a number is a perfect square: if you reach 0, it is; otherwise it isn't.