Can be written as the least square of the sum of two squares: 25=5? =3? +4? So 5 is the string in the smallest Pythagorean array. Count Karen. A pseudo prime number that at least conforms to 7n = 7 mod n. In decimal system, whether 25 is divisible can be determined by observing whether the last two digits of an integer are 25, 50, 75 or 00. Odd automorphic numbers, that is, numbers ending in 25 are multiplied, and the mantissa is still 25. Such as:12425× 31425 = 390455625. 2525×2525=6375625。 Multiply 25 by a number, and when the number is divided by 4, the remainder is 1, and the last two digits of the product are still 25, for example, 25×5= 125, 25×9=225, 25× 13=325, 25×1. In other words, any number ending in 25 can be divisible by 25. 2×5= 10，4×25= 100，8× 125 = 1000(xz×yz =(xy)z)。 The n power of 25 is a square number.