Set the upper end of the range no more than 100 whole numbers from the lower end to hopefully keep it from running ridiculously long (>36 hours).
Put the prize amount on a previously unfunded private key, and save that with the corresponding address. Sign a message containing just the random number that everyone's guessing at with that private key, then put ONLY the signature of the message in the OP (if the address is posted with the signature, people can flip through each number in the range to see which one verifies, and win the contest easily).
^ When the winner is declared, anyone can put the address, the signature of the message, and the winning number message (all provided in the declaration) into
https://insight.bitpay.com/messages/verify or their
BTC client, to verify the random number choice didn't change (assuming the OP timestamp doesn't show it was edited, suspiciously, since that's where the signature was first provided).
Link in the OP and frequently update a
Google Sheet that only you/consensus-trusted person can edit but everyone with the URL can view with columns: Number guessed, First to guess, Second to guess, Third to guess, etc.
^ Use the PAGES: [ALL] link when the topic goes over 1 page, to accurately put everyone's guesses in chronological order. And watch their timestamps for edit indication.
Set rules:
Each player must read the entire topic ([ALL] link) and the Google Sheet (linked in your OP), THEN reply to the topic with one number nobody else guessed already (a valid guess).
But if they are dyslexic, and their original guess was a second, third, etc. duplicate of someone else's and therefore invalid...
Players may post a reply with a valid guess below a quote of their original invalid guess.
After a player is the first to reply to the topic with one number nobody else guessed already (a valid guess), they cannot edit or delete their reply to guess a new one - the Google Sheet will lock in the first valid guesser's username for each number.