And what is the address, which holds the 4.87 BTC?
https://blockchain.info/address/1FLAMEN6rq2BqMnkUmsJBqCGWdwgVKcegdWhat are the possible ways to access the account, meaning what should the solution resemble?
Private keys in bitcoin are 256 bits (32 bytes):
https://en.bitcoin.it/wiki/Private_keyIn both base 64 and base 58 (6bits per character) that would require 43 characters.
In base 16 (4bits per character) that requires exactly 64 characters.
Private keys can also be encoded in a WIF format (
https://en.bitcoin.it/wiki/Wallet_import_format) that allows for validity checking. These are essentially the private key with 0x80 at the beginning and 4 checksum bits added at the end. Optionally 0x01 can be added at the end making for 296 and 304 bits respectively.
These most commonly appear as 51 or 52 characters in base 58.
With all that said I think it comes down to one of the following:
Find exactly 256, 296, or 304 0s and 1s.
Find 43, 51, or 52 groups of 6 bits.
Find 64, 74, or 76 groups of 4 bits.
Find 86, 99, or 102 groups of 3 bits.
Find 128, 148, or 152 groups of 2 bits.