I took the index on the words, transformed the quantity to binary, added three zeros, calculated the sha256 digest, took the initial Element of the hexadecimal to transform it to binary, added three zeros to your 8 digits from the binary and got 00000010011 which translates to 19 in decimal. https://geniusbookmarks.com/story18822465/not-known-factual-statements-about-bip39-explained