# Cannot find how to write infinity [duplicate]

I am new here. How do I write an infinity symbol above summation symbol. I do not know how to write formula on this site. How do I write series formula? I could figure out how to write summation, but how do I write infinity here above summation symbol? I could not find it. Thanks.

## marked as duplicate by T. Bongers, Asaf Karagila♦, user99914, José Carlos Santos, user223391 Feb 12 '18 at 21:15

To answer your specific question, we can do \infty to produce $\infty$ and \sum_{i=0}^{\infty}a_i to produce $\sum_{i=0}^{\infty}a_i$. Using two \\$ in a row, like this $$\sum_{i=0}^{\infty}a_i$$ produces the same equation, but set on it's own line $$\sum_{i=0}^{\infty}a_i$$