I took the index with the words, converted the variety to binary, included a few zeros, calculated the sha256 digest, took the primary part of the hexadecimal to convert it to binary, extra three zeros into the 8 digits with the binary and got 00000010011 which translates to 19 in https://followbookmarks.com/story18941101/ledger-seed-phrase-bip39-no-further-a-mystery