natural numbers symbol latex code example

Example 1: latex real number symbol

\documentclass{article}
\usepackage{amssymb}
\begin{document}
\begin{tabular}{ll}
Plain-\TeX{}:   & ${\rm I\!R}$\\
amssymb:        & $\mathbb{R}$
\end{tabular}
\end{document}

Example 2: natural numbers latex

\usepackage{amssymb}
$\mathbb{N}$

Example 3: complex numbers latex

\usepackage{amssymb}
$\mathbb{C}$

Example 4: llatex element of

A\in B % one stroke in middle