MathCastle
Counting & ProbabilitySuperchallengeRecursion, Catalan Numbers & Generating Functions

Recursion, Catalan Numbers & Generating Functions · Superchallenge problem

A mountain range is drawn with 77 upstrokes and 77 downstrokes: a path of 1414 unit diagonal steps that starts on the ground, ends on the ground, and never goes below it. A foothill is an upstroke from the ground immediately followed by a downstroke back to the ground. How many mountain ranges have no foothill?