I took the index from the words, transformed the quantity to binary, extra a few zeros, calculated the sha256 digest, took the very first Element of the hexadecimal to convert it to binary, additional three zeros to your 8 digits on the binary and got 00000010011 which translates to 19 https://captainbookmark.com/story18802464/the-fact-about-bip39-seed-phrase-word-list-that-no-one-is-suggesting