I took the index with the words, transformed the range to binary, additional three zeros, calculated the sha256 digest, took the 1st Component of the hexadecimal to transform it to binary, added a few zeros on the 8 digits of your binary and got 00000010011 which interprets to 19 in https://thebookpage.com/story4543511/5-simple-techniques-for-bip39-seed-phrase