C66 Teacher Hand in the Script

"Damn it, why is it so hard? "In the corner of the auditorium, Bai Chong was holding his head with both hands and his face was ashen.

He answered the first question very smoothly. It only took him half an hour to solve it, but when he saw the second question, he was stunned.

What the hell was this?

Orthodox number (An) = An + 1 = An -N1, an = N, and an + N