I took the index of your words, converted the quantity to binary, included three zeros, calculated the sha256 digest, took the 1st part of the hexadecimal to transform it to binary, included 3 zeros to your 8 digits of your binary and obtained 00000010011 which translates to 19 in decimal. https://thesocialcircles.com/story4625467/5-simple-techniques-for-bip39-word-list-pdf