MathCastle
Counting & ProbabilityChallengeAdvanced Number Theory

Advanced Number Theory · Challenge problem

A path from (0,0)(0,0) to (10,10)(10,10) consists of 2020 unit steps, each either to the right or up. Let NN be the number of such paths that never pass through a point (x,y)(x,y) with y−x≥3y - x \ge 3 (so the path never rises more than 22 above the diagonal y=xy = x). Find the remainder when NN is divided by 10001000.