>L.
   10 FOR loop%=0 TO 20
   20  PRINT loop%,(loop%+1) AND (NOT 3)
   30 NEXT
>RUN
         0         0
         1         0
         2         0
         3         4
         4         4
         5         4
         6         4
         7         8
         8         8
         9         8
        10         8
        11        12
        12        12
        13        12
        14        12
        15        16
        16        16
        17        16
        18        16
        19        20
        20        20