I took the index with the words, converted the selection to binary, included 3 zeros, calculated the sha256 digest, took the first A part of the hexadecimal to transform it to binary, additional 3 zeros towards the 8 digits in the binary and got 00000010011 which translates to 19 in https://ztndz.com/story21972706/bip39-seed-phrase-mnemonics-generator-an-overview