I took the index with the words, transformed the range to binary, extra 3 zeros, calculated the sha256 digest, took the main part of the hexadecimal to convert it to binary, included three zeros into the 8 digits from the binary and obtained 00000010011 which translates to 19 in decimal. https://wavesocialmedia.com/story4622593/a-review-of-bip39-phrase-list