You can continue this idea of symmetry for 50+ now that you got a way to get the first 50 squares. Simply subtract 50 from your given number and add the result to 25 for the left hand side and square it for the right hand side:
Example: 57²
Δ = 7
→ lhs: 25 + 7 = 32
→ rhs: 7² = 49
and you get 3249