I took the index in the words, converted the selection to binary, extra a few zeros, calculated the sha256 digest, took the first Element of the hexadecimal to convert it to binary, included 3 zeros into the 8 digits on the binary and obtained 00000010011 which interprets to 19 in https://wise-social.com/story5102908/the-fact-about-valid-bip39-seed-phrase-that-no-one-is-suggesting