20201209921 has 2 divisors, whose sum is σ = 20201209922. Its totient is φ = 20201209920.

The previous prime is 20201209877. The next prime is 20201209933. The reversal of 20201209921 is 12990210202.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19864083600 + 337126321 = 140940^2 + 18361^2 .

It is a cyclic number.

It is not a de Polignac number, because 20201209921 - 2¹⁵ = 20201177153 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 20201209921.

It is not a weakly prime, because it can be changed into another prime (20201209981) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10100604960 + 10100604961.

It is an arithmetic number, because the mean of its divisors is an integer number (10100604961).

Almost surely, 2^20201209921 is an apocalyptic number.

It is an amenable number.

20201209921 is a deficient number, since it is larger than the sum of its proper divisors (1).

20201209921 is an equidigital number, since it uses as much as digits as its factorization.

20201209921 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 spelling of 20201209921 in words is "twenty billion, two hundred one million, two hundred nine thousand, nine hundred twenty-one".