Bip39 last word checksum https://squareblogs.net/edelinepge/using-python-to-produce-a-bip39-mnemonic-a-developers-point-of-view Though it employs BIP32 system you can even now import BIP39 seeds into Electrum wallet. Also other than BIp32 There's BIP44 version which some wallet use for that generation of seeds. As opposed to standard wallets derived only from a seed phrase, passphrase... https://total-bookmark.com/story20557229/bip39-passphrase-github-helping-the-others-realize-the-advantages-of-bip39-passphrase-https-t-me-bip39-chat