Call an ordered triple (a, b, c) of integers feral if b-a, c-a and c-b are all prime. Find the number of feral triples where 1 \leq a<b<c \leq 20.
Call an ordered triple (a, b, c) of integers feral if b-a, c-a and c-b are all prime. Find the number of feral triples where 1 \leq a<b<c \leq 20.