I took the index with the words, transformed the range to binary, included a few zeros, calculated the sha256 digest, took the main Element of the hexadecimal to convert it to binary, added a few zeros to the eight digits of your binary and got 00000010011 which translates to 19 https://nybookmark.com/story20391254/ledger-seed-phrase-bip39-no-further-a-mystery