Thanks, all. That puts the runtimes on equal footing:
+ wc conjectures
125441818 125441818 6249180939 conjectures
+ rusage /home/jpl/src/grep-3.0/src/grep P[[:digit:]] conjectures
A[21]=11{11}:22<LP3
5.85 real 5.14 user 0.70 sys 0 pf 118 pr 0 sw 0 rb 0 wb 1 vcx 11 icx 2420 mx 0 ix 0 id 0 is
+ rusage /home/jpl/src/grep-3.0/src/grep P[[:digit:]] conjectures
A[21]=11{11}:22<LP3
5.77 real 5.10 user 0.67 sys 0 pf 121 pr 0 sw 0 rb 0 wb 1 vcx 7 icx 2492 mx 0 ix 0 id 0 is
+ rusage /home/jpl/src/grep-3.0/src/grep P[0-9] conjectures
A[21]=11{11}:22<LP3
5.80 real 5.15 user 0.62 sys 0 pf 119 pr 0 sw 0 rb 0 wb 1 vcx 1001 icx 2424 mx 0 ix 0 id 0 is