21312020021 has 2 divisors, whose sum is σ = 21312020022. Its totient is φ = 21312020020.

The previous prime is 21312020003. The next prime is 21312020033. The reversal of 21312020021 is 12002021312.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20025363121 + 1286656900 = 141511^2 + 35870^2 .

It is a cyclic number.

It is not a de Polignac number, because 21312020021 - 2²⁶ = 21244911157 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21312019978 and 21312020005.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21312020321) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10656010010 + 10656010011.

It is an arithmetic number, because the mean of its divisors is an integer number (10656010011).

Almost surely, 2^21312020021 is an apocalyptic number.

It is an amenable number.

21312020021 is a deficient number, since it is larger than the sum of its proper divisors (1).

21312020021 is an equidigital number, since it uses as much as digits as its factorization.

21312020021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 48, while the sum is 14.

Adding to 21312020021 its reverse (12002021312), we get a palindrome (33314041333).

The spelling of 21312020021 in words is "twenty-one billion, three hundred twelve million, twenty thousand, twenty-one".