I took the index with the words, converted the variety to binary, added a few zeros, calculated the sha256 digest, took the primary part of the hexadecimal to convert it to binary, included three zeros to your 8 digits on the binary and got 00000010011 which translates to 19 in https://socialtechnet.com/story4959685/helping-the-others-realize-the-advantages-of-bip39-mnemonic-phrase-tool