Bip39 or slip39 https://www.anobii.com/en/01000289012ff9b293/profile/activity Regardless that it employs BIP32 system you could nevertheless import BIP39 seeds into Electrum wallet. Also other than BIp32 There's BIP44 Model which some wallet use for your generation of seeds. For words that have only 3 letters, there isn't any 4th letter. For example Together https://letsbookmarkit.com/story20063552/bip39-react-bip39-compatible-wallet-can-be-fun-for-anyone-https-linktr-ee-bip39