# How to write mathematical symbols such as $\sum_{i=n}^\mathbb{N}$ with indices below/above the $\sum$ [duplicate]

I want to write:

$\cup_{n \in \mathbb{N}}$, and $\sum_{i=n}^\mathbb{N}$. But I want them the index to be above and below the symbol, not to the side, how do I fix this?

• Let me just say that using $\mathbb N$ as the upper bound for a sum is very unusual. I'd say that $\sum\limits_{i=n}^N$ or $\sum\limits_{i=n}^\infty$ are what I would have expected there. – Martin Sleziak Apr 29 '14 at 6:56
• @Martin: Or $\sum\limits_{n\in\Bbb N}$. – Asaf Karagila Apr 29 '14 at 6:57
• Please avoid doing this in titles. It takes too much vertical space on the homepage, and it's unfair to others. – Ayman Hourieh Apr 29 '14 at 11:45
• To expand on what @AymanHourieh wrote: There is a post about Guidelines for good use of $\LaTeX$ in question titles – Martin Sleziak Apr 29 '14 at 12:22

You can use \limits to get that as in $\sum\limits_{i=n}^\mathbb{N}\frac1{i^2}$. However, this severely messes with the interline spacing.
code: \sum\limits_{i=n}^\mathbb{N}\frac1{i^2}
You can also use \displaystyle as in $\displaystyle\sum_{i=n}^\mathbb{N}\frac1{i^2}$. However, this really messes with interline spacing.
code: \displaystyle\sum_{i=n}^\mathbb{N}\frac1{i^2}
• Considering the examples in the OP, it is also worth mentioning that \cup cannot be used together with limits, one has to use \bigcup instead: $\bigcup\limits_{n\in\mathbb N}$ $\bigcup\limits_{n\in\mathbb N}$. – Martin Sleziak Apr 28 '14 at 17:07
• @MartinSleziak: good point, I didn't notice they were using $\cup$. However, they could use $\operatorname{\cup}\limits_{i=1}^\infty$ or $\operatorname*{\cup}_{i=1}^\infty$. – robjohn Apr 28 '14 at 18:15