A row of Pascal's triangle

A row of Pascal's triangle

Every number in Pascal's triangle is the sum of the two numbers just above it, and every row starts and ends with 1.

Build the rows one at a time. A new row starts with 1, then adds each neighbouring pair of the previous row, row[i] + row[i + 1], and ends with 1. After n rounds, row is the answer. In China the same triangle is named after Yang Hui, who described it in 1261.