I took the index of your words, transformed the quantity to binary, added three zeros, calculated the sha256 digest, took the primary Element of the hexadecimal to convert it to binary, included three zeros for the eight digits of your binary and received 00000010011 which interprets to 19 in decimal. https://nybookmark.com/story20409210/considerations-to-know-about-bip39-word-list-pdf