I took the index on the words, transformed the selection to binary, included three zeros, calculated the sha256 digest, took the first A part of the hexadecimal to convert it to binary, added three zeros towards the 8 digits from the binary and received 00000010011 which translates to 19 in https://alphabookmarking.com/story18699135/getting-my-bip39-words-to-numbers-to-work