I have a silly script that tries to predict the challenge keys. I like to toy with this stuff.

If I pass it the sequence of known keys from #1 to #64, this is the prediction for #65:

Prediction: 3.05208467e+19 -> 1A78FD45E05A73800

Now passing it the sequence from #1 to #65:

Prediction: 4.73075146e+19 -> 290860DE1FB9B1000