13n2

13n2 is a notation commonly encountered in mathematics, particularly in combinatorics and calculus. It represents the binomial coefficient "13 choose 2". This signifies the number of ways to select 2 items from a set of 13 distinct items without regard to the order of selection.

The formula for calculating binomial coefficients is nCr = n! / (r! * (n-r)!), where 'n' is the total number of items and 'r' is the number of items to choose. For 13n2, this translates to 13! / (2! * (13-2)!) = 13! / (2! * 11!).

Calculating this value involves factorials. 13! is 13 * 12 * 11 * ... * 1, 2! is 2 * 1, and 11! is 11 * 10 * ... * 1. Simplifying the expression, we get (13 * 12) / (2 * 1), which equals 156 / 2, resulting in 78. Therefore, there are 78 ways to choose 2 items from a set of 13.

In calculus, 13n2 might appear as a coefficient in a Taylor series expansion or in the context of probability distributions, such as the binomial distribution where 'n' and 'k' are often used to denote parameters. The core concept remains the selection of a subset from a larger group.