[ ' [ 0 ]
     swap 1+ times
       [ dup -1 peek
         i^ 1+ mobius
         + join ]
     behead drop ]        is mertens   ( n --> [ )

  [ say "   "
    99 times
      [ dup i^ peek
        dup dup
        -1 > if sp
        abs 10 < if sp
        echo
        i^ 1+ 10 mod
        9 = if cr ]
     drop ]               is grid      ( [ -->   )

  [ 0 swap
    witheach
     [ 0 = + ] ]          is zeroes    ( [ --> n )

  [ 0 0
    rot witheach
      [ dup 0 =
        rot 0 !=
        and
        rot + swap ]
    drop ]                is crossings ( [ --> n )

  1000 mertens
  say "First 99 terms:"
  cr
  dup grid
  cr
  dup zeroes echo say " zeroes and "
  crossings  echo say " crossings"