Summing up some cubes I noticed that 13 + 23 + 33 + 43 = 100, which is 102. And the pattern held as I added more cubes (i.e., I kept getting squares). This is well known in the world of mathematics and number theory, but it was new to me. Extending the pattern:
And that makes these triangular numbers. And that means that every triangular number squared is the sum of cubes. It works both way in being interesting.