Nice. A unique year indeed, since the last one was 1936, 89 years ago. It's obvious to me now - that's 2025-(45*2-1) and I can picture a row and a column at the edges of a grid being removed, wth one cell being shared between the row and column. I think maybe at some point I saw that. 1600 and 2500 are more obvious, and 2050 is the midpoint between them linearly.

The others in Python:

    sum(range(1, 10))**2
    sum(n**3 for n in range(1, 10))