21123203021 has 4 divisors (see below), whose sum is σ = 21198374844. Its totient is φ = 21048031200.

The previous prime is 21123203011. The next prime is 21123203027. The reversal of 21123203021 is 12030232112.

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 10912100521 + 10211102500 = 104461^2 + 101050^2 .

It is a cyclic number.

It is not a de Polignac number, because 21123203021 - 2¹⁰ = 21123201997 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 (21123203027) 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, 37585490 + ... + 37586051.

It is an arithmetic number, because the mean of its divisors is an integer number (5299593711).

Almost surely, 2^21123203021 is an apocalyptic number.

It is an amenable number.

21123203021 is a deficient number, since it is larger than the sum of its proper divisors (75171823).

21123203021 is an equidigital number, since it uses as much as digits as its factorization.

21123203021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 75171822.

The product of its (nonzero) digits is 144, while the sum is 17.

Adding to 21123203021 its reverse (12030232112), we get a palindrome (33153435133).

The spelling of 21123203021 in words is "twenty-one billion, one hundred twenty-three million, two hundred three thousand, twenty-one".