Đặt A=12(5^2+1)(5^4+1)(5^8+1)(5^16+1)(5^32+1)(5^64+1)
-> 2A= 24(5^2+1)(5^4+1)(5^8+1)(5^16+1)(5^32+1)(5^64+1)
-> 2A= (5^2-1)(5^2+1)(5^4+1)(5^8+1)(5^16+1)(5^32+1)(5^64+1)
-> 2A= (5^4-1)(5^4+1)(5^8+1)(5^16+1)(5^32+1)(5^64+1)
-> 2A= (5^8-1)(5^8+1)(5^16+1)(5^32+1)(5^64+1)
-> 2A= (5^16-1)(5^16+1)(5^32+1)(5^64+1)
-> 2A= (5^32-1)(5^32+1)(5^64+1)
-> 2A= (5^64-1)(5^64+1)=5^128-1
-> A= (5^128-1)/2