$ seq 2 64 | xargs factor | awk '2 == NF { print $NF }' | xargs echo

2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61

 Name                    Last modified      Size  Description
 Parent Directory                             -   
 Makefile.make           2004-01-04 10:01   99   
 prime.c                 2004-01-04 10:01  293