Working in rows, from top to bottom, the sum of the digits in each row increases by 2 each time, from 8 to 16.

Working clockwise around the 3 triangles, the sum of the outer digits in each triangle is written in the centre of the triangle one place clockwise.

Numbers follow the sequence of Square Numbers, from 1 to 6, multiplying each one by 2.

As you move down, multiply each number by 2 and subtract 4.

The sum of the numbers along each side of the triangle is always 15.