Pascal’s triangle

										1
									1		1
								1		2		1
							1		3		3		1
						1		4		6		4		1
					1		5		10		10		5		1
				1		6		15		20		15		6		1
			1		7		21		35		35		21		7		1
		1		8		28		56		70		56		28		8		1
	1		9		36		84		126		126		84		36		9		1
1		10		45		120		210		252		210		120		45		10		1

Notation

$n \choose k$ is the mathematical symbol for the k^th entry of the n^th row of Pascal’s triangle, (counting from zero!)

${n \choose k}={\frac {n!}{k!(n-k)!}}$

${n \choose k}={n-1 \choose k-1}+{n-1 \choose k}$