\documentclass[12pt,a4paper]{article}
\usepackage[utf8]{inputenc}
\usepackage[french]{babel}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\usepackage{amsmath}
\usepackage{multicol}
\usepackage{pythontex}
\usepackage{nopageno}
\setlength{\parindent}{0pt}
\setlength{\columnseprule}{0.4pt}
\begin{document}
\begin{multicols}{4}
\begin{pycode}
import random

for n in range(91):
    a = random.randint(2,9)
    b = random.randint(2,9)
    c = a*b
    if (n%3 == 0):
        print('$\\ldots\\times',b,' = ',c,'$\\\\[1em]')
    else:
        if (n%3 == 1):
            print('$',a,'\\times\\ldots = ',c,'$\\\\[1em]')
        else:
            print('$',a,'\\times ',b,' = \\ldots$\\\\[1em]')
\end{pycode} 
\end{multicols}           
\end{document}