8420

8420 = 2 x 2 x 5 x 421.

8420 is the number of symmetric ways to fold a strip of 20 stamps (A001010).

8420 = 20³ + 20² + 20 (A027444 and A063012).

8420 has two representations as a sum of two squares: 8420 = 26² + 88² = 32² + 86².

8420 divides 29⁴ - 1.

Source: What's Special About This Number?