What is the Triangular number?
A number which can be represented by a triangular array of dots. 1, 3, 6, 10, are all triangular numbers.
The nth triangular number is n(n+1)/2.
All integer is the sum of at most 3 triangular numbers.
If t is a triangular number, 8t+1 is a square.
The square of the nth triangular number is equal to the sum of the first n cubes.
Certain triangular numbers are also squares, but no triangular number can be a third, fourth or fifth power.