You must generate a random 81 character seed using only A-Z and the number 9. It is imperative that your seed be an 81 character random assortment of A-Z and 9.
cat /dev/urandom |tr -dc A-Z9|head -c${1:-81}
cat /dev/urandom |LC_ALL=C tr -dc 'A-Z9' | fold -w 81 | head -n 1
(based on knarz seedgen)