I took the index from the words, transformed the amount to binary, included three zeros, calculated the sha256 digest, took the 1st Portion of the hexadecimal to convert it to binary, included three zeros to your eight digits on the binary and got 00000010011 which translates to 19 in decimal. https://zbookmarkhub.com/story19120208/a-review-of-bip39-phrase-list