Question 28
For n ≥ 3, the sequence of centred n-gon numbers is found by starting with a central dot, then adding layers consisting of n-gons of dots around this centre, where the number of dots on each side increases by 1 for each layer. For instance, the sequence of centred 7-gon numbers starts 1, 8, 22, 43, … as shown. What is the smallest n for which 2017 is in the sequence of centred n-gon numbers?
