Bip39 blockchain https://ameblo.jp/generate-bip39brooks/entry-12913353546.html While it uses BIP32 strategy you can however import BIP39 seeds into Electrum wallet. Also apart from BIp32 There's BIP44 version which some wallet use for the generation of seeds. For words that have only three letters, there is not any 4th letter. As an example With https://telegra.ph/Producing-Custom-Bitcoin-Addresses-A-Take-A-Look-At-BIP39-Strategies-06-28