Sửa đề:
A = 24.(5² + 1)(5⁴ + 1)(5⁸ + 1) ... (5¹²⁸ + 1)(5²⁵⁶ + 1)
= (5² - 1)(5² + 1)(5⁴ + 1)(5⁸ + 1)...(5¹²⁸ + 1)(5²⁵⁶ + 1)
= (5⁴ - 1)(5⁴ + 1)(5⁸ + 1)...(5¹²⁸ + 1)(5²⁵⁶ + 1)
= (5⁸ - 1)(5⁸ + 1)...(5¹²⁸ + 1)(5²⁵⁶ + 1)
= (5¹⁶ - 1)...(5¹²⁸ + 1)(5²⁵⁶ + 1)
= (5¹²⁸ - 1)(5¹²⁸ + 1)(5²⁵⁶ + 1)
= (5²⁵⁶ - 1)(5²⁵⁶ + 1)
= 5⁵¹² - 1