I took the index with the words, transformed the quantity to binary, added three zeros, calculated the sha256 digest, took the 1st part of the hexadecimal to convert it to binary, additional 3 zeros into the 8 digits of your binary and acquired 00000010011 which interprets to 19 in decimal. https://sound-social.com/story8968175/5-essential-elements-for-bip39-explained