I took the index on the words, transformed the amount to binary, included 3 zeros, calculated the sha256 digest, took the first Section of the hexadecimal to convert it to binary, included three zeros on the 8 digits of your binary and received 00000010011 which translates to 19 in decimal. https://hypebookmarking.com/story19389164/the-2-minute-rule-for-bip39-all-words