In all seriousness, how many (sticking to averages of math / the curve) BY8GQbnueY prefixes are in a 66 bit space? I come up with 171. Is that correct or close to what others think / know?
And for the prefix, BY8GQbnue, a little less than 10k inside a 66 bit space?
If there are no different ideas, different works, this competition cannot progress.
I think the issue with your statement, is, others have tried this method, and to my knowledge, no one has found the key, using the same or similar methods. But maybe you will be the first!
Not sure why it's useful to know how many prefixes of exactly 10 matching chars exist within the 66 key space, since public keys are distributed randomly within the curve and since the ripemd hashing loses information anyways I would not consider this helpful in any way. However, log2(58) = 5.858 * 10 = 58.57 bits, so for 66 bit range 66 - 58.57 = 7.43 so 2^7.43 equals approx. 172 possible prefixes.