I took the index from the words, transformed the variety to binary, added a few zeros, calculated the sha256 digest, took the 1st Element of the hexadecimal to transform it to binary, included 3 zeros for the 8 digits from the binary and received 00000010011 which interprets to 19 in https://bookmarkeasier.com/story18689922/the-fact-about-valid-bip39-seed-phrase-that-no-one-is-suggesting