I took the index from the words, transformed the quantity to binary, extra a few zeros, calculated the sha256 digest, took the initial Section of the hexadecimal to transform it to binary, extra 3 zeros to your 8 digits with the binary and obtained 00000010011 which interprets to 19 in https://linkingbookmark.com/story19368521/an-unbiased-view-of-bip39-seed-phrase-github