I took the index of your words, transformed the quantity to binary, additional 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 on the binary and obtained 00000010011 which interprets to 19 in decimal. https://ledbookmark.com/story5144640/considerations-to-know-about-bip39-seed-phrase-generator