I'm not quite sure, but for programming reasons I'm seriously expecting the maximum number to be 65535.
It's a ridiculous oversight to not state the maximum number on the site. Also, the reasons why the number is so large is major geekery
The range is 0 to 65535 inclusive.
In PHP, the magic number can be calculated as:
hexdec(substr(hash_hmac('sha512', "$txid:$nout", $secret), 0, 4))
ie. the first 4 hex characters of the sha512 hmac of (the transaction id, a colon, and the output number) with the daily secret. As a decimal.
There's
a webpage that independently calculates your random numbers given the daily secret and the bet transaction ID.
I never noticed that it doesn't state the range of the random number anywhere on site before. That is surprising.
If the range wasn't so big, they couldn't offer a 64000x payout unless they generated multiple numbers per bet.