205821391 has 2 divisors, whose sum is σ = 205821392. Its totient is φ = 205821390.

The previous prime is 205821389. The next prime is 205821449. The reversal of 205821391 is 193128502.

205821391 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 205821391 - 2¹ = 205821389 is a prime.

Together with 205821389, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (205821691) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 102910695 + 102910696.

It is an arithmetic number, because the mean of its divisors is an integer number (102910696).

Almost surely, 2^205821391 is an apocalyptic number.

205821391 is a deficient number, since it is larger than the sum of its proper divisors (1).

205821391 is an equidigital number, since it uses as much as digits as its factorization.

205821391 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 4320, while the sum is 31.

The square root of 205821391 is about 14346.4766057733. The cubic root of 205821391 is about 590.4233206354.

Adding to 205821391 its reverse (193128502), we get a palindrome (398949893).

The spelling of 205821391 in words is "two hundred five million, eight hundred twenty-one thousand, three hundred ninety-one".