I took the index with the words, transformed the range to binary, included a few zeros, calculated the sha256 digest, took the first Portion of the hexadecimal to convert it to binary, added three zeros on the eight digits of your binary and got 00000010011 which translates to 19 in https://mysocialquiz.com/story4281348/the-ultimate-guide-to-bip39-seed-phrase-github