NRICH (University of Cambridge)
Can you see how to build a harmonic triangle? Can you work out the next two rows?
NRICH (University of Cambridge)
Take a triangular number, multiply it by 8 and add 1. What is special about your answer? Can you prove it?
NRICH (University of Cambridge)
Triangular numbers can be represented by a triangular array of squares. What do you notice about the sum of identical triangle numbers?
National Council of Teachers of Mathematics
Order the digits 1 through 9 so that the sum of any two adjacent numbers is a triangular number.
