Question 356934
The values of A, B, C are guided by the equation {{{26A - 4B - 7C = 0}}}.  We only need to consider i) odd values for B and even values for C, and 
ii) even values for B and even values for C.
Only 3 ordered triples (A, B, C)will satisfy the constraint equation above:
(2,6,4), (1,3,2), and (3,9, 6).  Therefore the largest n is 396.