Bip39 numbers https://unsplash.com/@morganvmyg Despite the fact that it takes advantage of BIP32 method you can nevertheless import BIP39 seeds into Electrum wallet. Also apart from BIp32 There exists BIP44 version which some wallet use with the generation of seeds. For words that only have three letters, there's no 4th letter. https://files.fm/u/2eemhhak2q#design