I took the index of your words, converted the range to binary, added three zeros, calculated the sha256 digest, took the 1st A part of the hexadecimal to transform it to binary, additional 3 zeros for the eight digits on the binary and acquired 00000010011 which translates to 19 in https://cruxbookmarks.com/story18892659/the-fact-about-valid-bip39-seed-phrase-that-no-one-is-suggesting