21128958391 has 2 divisors, whose sum is σ = 21128958392. Its totient is φ = 21128958390.

The previous prime is 21128958371. The next prime is 21128958439. The reversal of 21128958391 is 19385982112.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21128958391 - 2²³ = 21120569783 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21128958371) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10564479195 + 10564479196.

It is an arithmetic number, because the mean of its divisors is an integer number (10564479196).

Almost surely, 2^21128958391 is an apocalyptic number.

21128958391 is a deficient number, since it is larger than the sum of its proper divisors (1).

21128958391 is an equidigital number, since it uses as much as digits as its factorization.

21128958391 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 311040, while the sum is 49.

The spelling of 21128958391 in words is "twenty-one billion, one hundred twenty-eight million, nine hundred fifty-eight thousand, three hundred ninety-one".