I took the index in the words, transformed the range to binary, included a few zeros, calculated the sha256 digest, took the first A part of the hexadecimal to convert it to binary, additional three zeros for the 8 digits with the binary and obtained 00000010011 which interprets to 19 https://travialist.com/story9161575/bip39-seed-phrase-mnemonics-generator-an-overview