245821 has 2 divisors, whose sum is σ = 245822. Its totient is φ = 245820.

The previous prime is 245789. The next prime is 245849. The reversal of 245821 is 128542.

245821 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 164025 + 81796 = 405^2 + 286^2 .

It is a cyclic number.

It is not a de Polignac number, because 245821 - 2⁵ = 245789 is a prime.

It is an Ulam number.

It is a nialpdrome in base 12.

It is a junction number, because it is equal to n+sod(n) for n = 245792 and 245801.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (245851) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 122910 + 122911.

It is an arithmetic number, because the mean of its divisors is an integer number (122911).

2²⁴⁵⁸²¹ is an apocalyptic number.

It is an amenable number.

245821 is a deficient number, since it is larger than the sum of its proper divisors (1).

245821 is an equidigital number, since it uses as much as digits as its factorization.

245821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 640, while the sum is 22.

The square root of 245821 is about 495.8033884515. The cubic root of 245821 is about 62.6430642720.

The spelling of 245821 in words is "two hundred forty-five thousand, eight hundred twenty-one".