To place the labels "m = 2", "p = 3" and "m + p = 2 + 3" as in the attached figure, I made some tests but the result is not yet the one expected. Is there a more rigorous method ?

[![enter image description here](https://i.stack.imgur.com/Wo22y.jpg)](https://i.stack.imgur.com/Wo22y.jpg)

```
  \documentclass[border=10pt]{standalone}
  \usepackage{unicode-math}
  \setmainfont{XITS}
  \setmathfont{XITS Math}
  \usepackage{pgfplots}
  \usepackage{mathrsfs}
  \pgfplotsset{compat=1.16}
  \usetikzlibrary{intersections}
  \usepgfplotslibrary{fillbetween}
  \begin{document}
  \begin{tikzpicture}
  \begin{axis}[
  x=1cm,y=1cm,
  xtick={0,1,...,7},ytick={0,1,...,6},
  ymin=-2.5,ymax=7,xmin=-1,xmax=8,
  ymin=-2.5,
  axis on top=false,
  enlargelimits=false,
  axis x line=middle,
  axis y line=middle,
  tick align=outside,
  tickwidth=0.12cm,
  xticklabels={0,1,\empty,\empty,\empty,\empty,\empty},
  yticklabels={0,1,\empty,\empty,\empty,\empty},
  major tick style = {thick, black},
  axis line style = ultra thick,
  x tick label style={
  /pgf/number format/1000 sep={}
  },
  extra x ticks={8},
  extra x tick label={\null},
  extra y ticks={7},
  extra y tick label={\null},
  extra tick style={tick style={draw=none}},
  xlabel=,ylabel=,
  every axis x label/.style=
  {
  at={(ticklabel* cs:1)},
  anchor=west
  },
  every axis y label/.style=
  {
  at={(ticklabel* cs:1)},
  anchor=south
  },
  >=stealth,
 grid=none]

\addplot+[
  mark=+,
  only marks,
  mark options={thick,black}
     ] 
  coordinates
  {(0,1) (1,1.3) (2,1.69) (3,2.197) (4,2.8561) (5,3.71293) (6,4.826809) (7,6.2748517) (8,8.157307209)};

 \draw[black,->,thick] (2,0)-- node[above,rotate=90]{$u_2$} (2,1.69);
 \draw[black,->,thick] (3,0)-- node[above,rotate=90]{$u_3$} (3,2.197);
 \draw[black,->,thick] (5,0)-- node[above,rotate=90]{$u_2 \times u_3$}(5,3.71293);  

 \node[below,black,rotate=45] at (2,-0.4){$m=2$};
 \node[below,black,rotate=45] at (3,-0.4){$p=3$};
 \node[below,black,rotate=45] at (4,-0.8){$m+p=2+3$};
 \node[right,black] at (6,4.826809) {$\mathcal{C}_{u_n}$};
 \node[below left=2pt] at (0,0){$0$};

 \end{axis}                  
 \end{tikzpicture}
 \end{document}

```

[![enter image description here](https://i.stack.imgur.com/PUCrG.png)](https://i.stack.imgur.com/PUCrG.png)