2021209921 has 2 divisors, whose sum is σ = 2021209922. Its totient is φ = 2021209920.

The previous prime is 2021209919. The next prime is 2021210011. The reversal of 2021209921 is 1299021202.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1071645696 + 949564225 = 32736^2 + 30815^2 .

It is a cyclic number.

It is not a de Polignac number, because 2021209921 - 2¹ = 2021209919 is a prime.

Together with 2021209919, it forms a pair of twin primes.

It is a self number, because there is not a number n which added to its sum of digits gives 2021209921.

It is not a weakly prime, because it can be changed into another prime (2021209901) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1010604960 + 1010604961.

It is an arithmetic number, because the mean of its divisors is an integer number (1010604961).

Almost surely, 2^2021209921 is an apocalyptic number.

It is an amenable number.

2021209921 is a deficient number, since it is larger than the sum of its proper divisors (1).

2021209921 is an equidigital number, since it uses as much as digits as its factorization.

2021209921 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1296, while the sum is 28.

The square root of 2021209921 is about 44957.8682879871. The cubic root of 2021209921 is about 1264.3592021858.

The spelling of 2021209921 in words is "two billion, twenty-one million, two hundred nine thousand, nine hundred twenty-one".