NCERT Example - Lockers open - A Square and A Cube

Question: In the 100-locker puzzle, which lockers remain open at the end? Which lockers are toggled exactly twice?

Answer: Open lockers: 1, 4, 9, 16, 25, 36, 49, 64, 81, 100. Visited twice: prime numbers (2, 3, 5, 7, 11, ...).

Full step-by-step NCERT solution with diagrams on Something by Zero.