# draw a circle - latex code

I want to create the following picture, how should i proceed?

Thanks!

The following example uses an uniform distribution of the points/angles.

\documentclass{article}
\usepackage{tikz}

\begin{document}
\begin{tikzpicture}
\draw
;
% Full circle evenly divided into 14 pieces
\foreach \i in {0, ..., 3, 12, 13} {
(M) +(90 - \i * 360/14:\Radius) circle[]
}
;
\path
\foreach \i/\a in {0/1, 1/2, 2/3, 3/4, 12/20, 13/21} {
(M) -- node[pos=.8] {$a_{\a}$} +(90 - \i * 360/14:\Radius)
}
;