That's an interesting idea, but I'm not sure how the "without I/O" hint applies to using a phone keypad?
I'd suggest trying my method above in the first instance, by concatenating your 27 digit number with the 21 digit prime (both before and afterwards) and hashing them with SHA256 to get a private key. I would try it but I'm away from home and on mobile at the moment, and don't really fancy trying to do it manually on my phone.
Phemex made another tweet yesterday, saying they will release the final clue to the puzzle on Friday: https://twitter.com/Phemex_official/status/1228318202247237632
I'd suggest trying my method above in the first instance, by concatenating your 27 digit number with the 21 digit prime (both before and afterwards) and hashing them with SHA256 to get a private key. I would try it but I'm away from home and on mobile at the moment, and don't really fancy trying to do it manually on my phone.
Phemex made another tweet yesterday, saying they will release the final clue to the puzzle on Friday: https://twitter.com/Phemex_official/status/1228318202247237632