I took the index on the words, transformed the variety to binary, included three zeros, calculated the sha256 digest, took the primary part of the hexadecimal to transform it to binary, included three zeros to your eight digits on the binary and got 00000010011 which interprets to 19 in decimal. https://socialupme.com/story4338054/5-simple-techniques-for-bip39-word-list-pdf