I took the index from the words, transformed the variety to binary, added 3 zeros, calculated the sha256 digest, took the first part of the hexadecimal to transform it to binary, included 3 zeros to the 8 digits of your binary and received 00000010011 which translates to 19 in decimal. https://mylittlebookmark.com/story5124854/5-essential-elements-for-bip39-explained