I took the index from the words, transformed the range to binary, added three zeros, calculated the sha256 digest, took the first Section of the hexadecimal to transform it to binary, additional a few zeros on the 8 digits of your binary and obtained 00000010011 which translates to 19 in https://webnowmedia.com/story5017458/getting-my-bip39-words-to-numbers-to-work