390821 has 2 divisors, whose sum is σ = 390822. Its totient is φ = 390820.

The previous prime is 390809. The next prime is 390829. The reversal of 390821 is 128093.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 390625 + 196 = 625^2 + 14^2 .

It is a cyclic number.

It is not a de Polignac number, because 390821 - 2¹⁰ = 389797 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (390829) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 195410 + 195411.

It is an arithmetic number, because the mean of its divisors is an integer number (195411).

2³⁹⁰⁸²¹ is an apocalyptic number.

It is an amenable number.

390821 is a deficient number, since it is larger than the sum of its proper divisors (1).

390821 is an equidigital number, since it uses as much as digits as its factorization.

390821 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 432, while the sum is 23.

The square root of 390821 is about 625.1567803359. The cubic root of 390821 is about 73.1126677038.

The spelling of 390821 in words is "three hundred ninety thousand, eight hundred twenty-one".