I took the index of your words, converted the quantity to binary, additional three zeros, calculated the sha256 digest, took the 1st part of the hexadecimal to transform it to binary, included three zeros towards the 8 digits from the binary and received 00000010011 which interprets to 19 in decimal. https://privatebookmark.com/story18948739/the-ultimate-guide-to-bip39-seed-phrase-mnemonics-generator