I took the index of the words, transformed the range to binary, extra a few zeros, calculated the sha256 digest, took the main part of the hexadecimal to convert it to binary, additional three zeros into the 8 digits on the binary and got 00000010011 which interprets to 19 in https://madbookmarks.com/story19141608/bip39-seed-phrase-mnemonics-generator-an-overview