\documentclass{article}
\usepackage[paperheight=74mm,paperwidth=105mm,margin=4mm]{geometry}
\pagenumbering{gobble}
\usepackage{unicode-math}
\begin{document}
$$
p_n = 1 + \sum_{i=1}^{2^n} \left\lfloor \left(\frac{n}{\sum_{j=1}^i \left\lfloor \cos^2\left(\pi \frac{(j-1)! + 1}{j}\right) \right\rfloor}\right)^{\frac{1}{n}} \right\rfloor
$$
\end{document}
