I took the index in the words, converted the range to binary, added 3 zeros, calculated the sha256 digest, took the 1st Component of the hexadecimal to convert it to binary, added a few zeros on the eight digits in the binary and obtained 00000010011 which translates to 19 in https://socialwebnotes.com/story4194196/a-secret-weapon-for-bip39-words-to-numbers