I took the index with the words, transformed the quantity to binary, extra three zeros, calculated the sha256 digest, took the primary part of the hexadecimal to convert it to binary, included 3 zeros to the 8 digits of your binary and received 00000010011 which interprets to 19 in decimal. https://webookmarks.com/story4564783/5-essential-elements-for-bip39-explained