[racket] Postfix hash syntax?

Hi,

I've been wondering what the postfix hash syntax does. This is what
happens when I append a # to an integer:

    > 9#
    90.0
    > 9##
    900.0
    > 9#####
    900000.0

Floating point numbers stay the same:

    > 22.3#
    22.3
    > 22.3##
    22.3
    > 22.3###
    22.3

I can't find this syntax in either the Racket Guide or the Reference.
In fact, I accidentally stumbled upon this behavior when a friend
mistyped 53 as "5#".

Thanks.

-- 
Ankur Sethi
(GeneralMaximus on IRC and elsewhere)