When playing with the maximum initial bet of 0.2 BTC in the 21 bomb game, 8 coins need to be found to win the 0.5 BTC bonus.
To get 8 coins on the 21 Bomb game is a 1 in 30.5234 chance by my calcs. Using the max bet of 0.2 Bitcoins, 30.5234*0.2 = 6.0147 Bitcoins.
This means to hit get 8 Coins in the 21 Bomb Game betting with 0.2 Bitcoins it would cost on average 6.1047 Bitcoins to win it.
As the amount won from 8 coins is 5.6331 and the prize money is 0.5 Bitcoins, you would win a total of 6.1331 Bitcoins
This means the house edge would be slightly negative playing like this. Where ((6.1331-6.1047)/ (6.1047))*100 is the new house edge. Which means the house edge would be -0.4652%
Can anyone check that?