tl;dr: The author rediscovered a 10-year-old Project Euler repo and found that Problem 15 (counting lattice paths in a grid) was solved not with code but with a text file recognizing the answer as the binomial coefficient (2n choose n). They reflect that today they'd reach for brute force, memoization, or just hand it to an AI, lamenting the loss of the mathematical intuition their student self once had.