I took the index of your words, converted the range to binary, added 3 zeros, calculated the sha256 digest, took the first Section of the hexadecimal to convert it to binary, added 3 zeros to the eight digits from the binary and obtained 00000010011 which interprets to 19 in decimal. https://bookmarksurl.com/story4478666/bip39-seed-phrase-mnemonics-generator-an-overview