21891428821 has 2 divisors, whose sum is σ = 21891428822. Its totient is φ = 21891428820.

The previous prime is 21891428803. The next prime is 21891428857. The reversal of 21891428821 is 12882419812.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21812040721 + 79388100 = 147689^2 + 8910^2 .

It is a cyclic number.

It is not a de Polignac number, because 21891428821 - 2³¹ = 19743945173 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21891528821) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10945714410 + 10945714411.

It is an arithmetic number, because the mean of its divisors is an integer number (10945714411).

Almost surely, 2^21891428821 is an apocalyptic number.

It is an amenable number.

21891428821 is a deficient number, since it is larger than the sum of its proper divisors (1).

21891428821 is an equidigital number, since it uses as much as digits as its factorization.

21891428821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 147456, while the sum is 46.

Subtracting from 21891428821 its reverse (12882419812), we obtain a palindrome (9009009009).

The spelling of 21891428821 in words is "twenty-one billion, eight hundred ninety-one million, four hundred twenty-eight thousand, eight hundred twenty-one".