I took the index of your words, converted the amount to binary, extra 3 zeros, calculated the sha256 digest, took the initial Element of the hexadecimal to transform it to binary, included three zeros for the 8 digits in the binary and received 00000010011 which translates to 19 in decimal. https://loanbookmark.com/story19027674/the-basic-principles-of-bip39-passphrase-generator