I took the index with the words, converted the range to binary, included three zeros, calculated the sha256 digest, took the primary Component of the hexadecimal to transform it to binary, extra 3 zeros to your 8 digits on the binary and received 00000010011 which interprets to 19 in decimal. https://bookmarkassist.com/story18741935/top-guidelines-of-bip39-word-list-pdf