I took the index from the words, converted the variety to binary, added 3 zeros, calculated the sha256 digest, took the first part of the hexadecimal to convert it to binary, included three zeros to your eight digits of your binary and received 00000010011 which translates to 19 in decimal. https://ragingbookmarks.com/story19030568/considerations-to-know-about-bip39-word-list-pdf