syntax problem with cron

[Steven Stern]

I'm having a problem running a command from cron that works well from the
command line.

The cron line is

  1 * * * * sleep $[ $RANDOM % 1800 ] ;/usr/bin/freshclam --quiet

When run from a /bin/sh command line, it works as expected.

When run from cron, I get an email with:

  /bin/sh: -c: line 1: unexpected EOF while looking for matching `]'
  /bin/sh: -c: line 2: syntax error: unexpected end of file

What am I missing?
-- 
  Steve