Narayana number

In combinatorics, the Narayana numbers ${\displaystyle \operatorname {N} (n,k),n\in \mathbb {N} ^{+},1\leq k\leq n}$ form a triangular array of natural numbers, called the Narayana triangle, that occur in various counting problems. They are named after Canadian mathematician T. V. Narayana (1930–1987).

Narayana number

Named after	Tadepalli Venkata Narayana
No. of known terms	infinity
Formula	${\displaystyle \operatorname {N} (n,k)={\frac {1}{n}}{n \choose k}{n \choose k-1}}$
OEIS index	A001263 Triangle of Narayana