Bip39 seed generator https://ameblo.jp/generate-bip39brooks/entry-12913353546.html Although it makes use of BIP32 technique you could even now import BIP39 seeds into Electrum wallet. Also other than BIp32 there is BIP44 Model which some wallet use for the era of seeds. For words that have only three letters, there isn't any 4th letter. https://nimmansocial.com/story10348615/bip39-finder-not-known-factual-statements-about-bip39-word-list-txt-https-t-me-bip39-chat