21243400021 has 4 divisors (see below), whose sum is σ = 21243952044. Its totient is φ = 21242848000.

The previous prime is 21243400019. The next prime is 21243400033. The reversal of 21243400021 is 12000434212.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 4887547921 + 16355852100 = 69911^2 + 127890^2 .

It is a cyclic number.

It is not a de Polignac number, because 21243400021 - 2¹ = 21243400019 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21243400051) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 213580 + ... + 296821.

It is an arithmetic number, because the mean of its divisors is an integer number (5310988011).

Almost surely, 2^21243400021 is an apocalyptic number.

It is an amenable number.

21243400021 is a deficient number, since it is larger than the sum of its proper divisors (552023).

21243400021 is an equidigital number, since it uses as much as digits as its factorization.

21243400021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 552022.

The product of its (nonzero) digits is 384, while the sum is 19.

Adding to 21243400021 its reverse (12000434212), we get a palindrome (33243834233).

The spelling of 21243400021 in words is "twenty-one billion, two hundred forty-three million, four hundred thousand, twenty-one".