Looking at the diagram in rows, the central circle equals half the sum of the numbers in the other circles to the left and right of the centre.

The number at the centre of each triangle equals the sum of the lower two numbers minus the top number.

As you move diagonally down, numbers follow the sequence of Prime Numbers.

Starting bottom left and moving clockwise around the triangle, numbers follow the sequence of Square Numbers.

Working from top to bottom, double each number and subtract 1, then 2, then 3 etc.