\documentclass[12pt,a4paper]{article}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{amsmath}
\usepackage{dirtytalk}
\usepackage{blindtext}
\usepackage{graphics}
\usepackage{tgbonum}
\usepackage{tikz}
\usepackage{mathtools}
\usepackage{flexisym}
\usepackage{cite}
\usepackage{nth}
\usepackage{amsthm}
\begin{document}
$$1,\underbrace{\frac{1}{2^2},\frac{1}{2^2},\frac{1}{2^2},\frac{1}{2^2}}_\text{2^2 times},\frac{1}{6^2},\frac{1}{8^2},\frac{1}{9^2},\frac{1}{10^2},\frac{1}{11^2},\frac{1}{12^2},\frac{1}{13^2},
\underbrace{\frac{1}{14^2},\frac{1}{14^2},\cdots,\frac{1}{14^2}}_\text{ times},\cdots$$
\end{document}
I am trying to write under braces. But it is not coming. Please help

2^2andtimes. Either you write2^2\text{ times}or (IMO better)\text{$2^2$ times}. – campa Aug 19 '19 at 12:45\textwould work in a subscript even without braces. But I completely agree that in most cases one must put them. – campa Aug 19 '19 at 13:19