s

1

2

3

$X_{\alpha }$

${\mathbb{Z}}_7$ , $F_{14}$ , $F_{21}$ , $F_{21}$ , $F_{21}\times {\mathbb{Z}}_3$

$F_{42}$ , $F_{42}\times {\mathbb{Z}}_2$ , $F_{42}\times {\mathbb{Z}}_3$

$F_{42}\times {\mathbb{Z}}_6$