Narayana number

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

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).