391028821 has 2 divisors, whose sum is σ = 391028822. Its totient is φ = 391028820.

The previous prime is 391028789. The next prime is 391028863. The reversal of 391028821 is 128820193.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 388641796 + 2387025 = 19714^2 + 1545^2 .

It is a cyclic number.

It is not a de Polignac number, because 391028821 - 2⁵ = 391028789 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (391028621) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 195514410 + 195514411.

It is an arithmetic number, because the mean of its divisors is an integer number (195514411).

Almost surely, 2^391028821 is an apocalyptic number.

It is an amenable number.

391028821 is a deficient number, since it is larger than the sum of its proper divisors (1).

391028821 is an equidigital number, since it uses as much as digits as its factorization.

391028821 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 6912, while the sum is 34.

The square root of 391028821 is about 19774.4486901658. The cubic root of 391028821 is about 731.2562474836.

The spelling of 391028821 in words is "three hundred ninety-one million, twenty-eight thousand, eight hundred twenty-one".