An investigation involving adding and subtracting sets of consecutive numbers. Lots to find out, lots to explore.
Choose any three by three square of dates on a calendar page...
Can you create a Latin Square from multiples of a six digit number?
The formula which gives in terms of is $C= \pi \times d$ , so the graph of C versus d is a straight line which passes through the origin.
This problem is taken from the UKMT Mathematical Challenges.