I took the index with the words, transformed the number to binary, extra three zeros, calculated the sha256 digest, took the initial Element of the hexadecimal to transform it to binary, added three zeros for the eight digits of your binary and got 00000010011 which translates to 19 in decimal. https://isocialfans.com/story4264998/the-fact-about-valid-bip39-seed-phrase-that-no-one-is-suggesting