Evaluate the sum of k squared for k running from 3 to 7.

1. The lower limit is 3 and the upper limit is 7, so the index takes the values 3, 4, 5, 6 and 7. 2. Squaring each gives 9, 16, 25, 36 and 49. 3. Adding them gives 9 + 16 = 25, then 25 + 25 = 50, then 50 + 36 = 86, then 86 + 49 = 135. 4. So the sum is 135. 5. Starting the index at 1 instead would add 1 and 4 as well, giving 140, which is the trap set by a lower limit other than 1. _Source: OpenStax Algebra and Trigonometry (CC BY 4.0), Ch 13 "Sequences, Probability and Counting Theory", section 13.4 Series and Their Notations_