The sum of the sequence beginning word 9 and continuing to word 15 is 1875. This may be expressed as 3x625 - 625 itself being 25x25, or 25^2. All this suggests the insertion of a rhombus of 625 at each vertex of our outline triangle, thus:
Observe that the inner vertices of these rhombi intersect at the centroid of the triangle - and therefore that each requires to be counted to arrive at the total, 1875.
Of further interest here is the fact that each of the trio of smaller triangles generated in this construction has the capacity 276 (see Acts 27:37, 44).