What Does the Notation \(\sum_{n=2}^{\infty} \binom{n}{2} z^{n}\) Represent?

[geft]

$$\sum_{n=2}^{\infty} \begin{pmatrix}<br /> {n}\\ <br /> {2}<br /> \end{pmatrix} z^{n}$$

 

[Office_Shredder]

Which part is confusing you?

 

[geft]

It's supposed to be a power series, but I don't understand how to decipher the brackets.

 

[micromass]

It's a binomial coefficient. It's defined as

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

See http://en.wikipedia.org/wiki/Binomial_coefficient

 

[geft]

Many thanks!