I took the index with the words, transformed the number to binary, added three zeros, calculated the sha256 digest, took the initial Component of the hexadecimal to convert it to binary, additional 3 zeros to your 8 digits from the binary and obtained 00000010011 which interprets to 19 in decimal. https://thesocialroi.com/story8569339/bip39-phrase-generator-can-be-fun-for-anyone