I took the index of your words, transformed the selection to binary, additional three zeros, calculated the sha256 digest, took the primary Portion of the hexadecimal to transform it to binary, included three zeros into the 8 digits from the binary and received 00000010011 which translates to 19 in decimal. https://bookmarkstown.com/story19171591/getting-my-bip39-words-to-numbers-to-work