The encryption method is extremely simple and the first letter is already in plaintext (the character number that is).
The plaintext is plain english.
[79, 32, 79, 39, 45, 39, 112, 21, 50, 64, 37, 5, 107, 4, 36, 87, 35, 81, 48, 94, 57, 92, 46, 93, 125, 9, 102, 70, 42, 69, 51, 86, 92, 5, 106...