21311320021 has 4 divisors (see below), whose sum is σ = 21311615052. Its totient is φ = 21311024992.

The previous prime is 21311319989. The next prime is 21311320039. The reversal of 21311320021 is 12002311312.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 4954188996 + 16357131025 = 70386^2 + 127895^2 .

It is a cyclic number.

It is not a de Polignac number, because 21311320021 - 2⁵ = 21311319989 is a prime.

It is a super-2 number, since 2×21311320021² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21311319977 and 21311320004.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21311320081) 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, 41961 + ... + 210673.

It is an arithmetic number, because the mean of its divisors is an integer number (5327903763).

Almost surely, 2^21311320021 is an apocalyptic number.

It is an amenable number.

21311320021 is a deficient number, since it is larger than the sum of its proper divisors (295031).

21311320021 is a wasteful number, since it uses less digits than its factorization.

21311320021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 295030.

The product of its (nonzero) digits is 72, while the sum is 16.

Adding to 21311320021 its reverse (12002311312), we get a palindrome (33313631333).

The spelling of 21311320021 in words is "twenty-one billion, three hundred eleven million, three hundred twenty thousand, twenty-one".