Significados de triangular numbers en inglés

Now for a little puzzle in triangular numbers.

Every whole number is either triangular , or the sum of two triangular numbers or the sum of three triangular numbers.

The analogous series for triangular numbers is 1, 3, 6, 1, 6, 3, 1, 9, 9.

But indeed unity is triangular ; for every triangular number ( Triangular numbers are those of which equilateral triangles can be formed in this way: