20881921 has 2 divisors, whose sum is σ = 20881922. Its totient is φ = 20881920.

The previous prime is 20881919. The next prime is 20881963. The reversal of 20881921 is 12918802.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 10890000 + 9991921 = 3300^2 + 3161^2 .

It is a cyclic number.

It is not a de Polignac number, because 20881921 - 2¹ = 20881919 is a prime.

Together with 20881919, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (20881901) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10440960 + 10440961.

It is an arithmetic number, because the mean of its divisors is an integer number (10440961).

Almost surely, 2^20881921 is an apocalyptic number.

It is an amenable number.

20881921 is a deficient number, since it is larger than the sum of its proper divisors (1).

20881921 is an equidigital number, since it uses as much as digits as its factorization.

20881921 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2304, while the sum is 31.

The square root of 20881921 is about 4569.6740583985. The cubic root of 20881921 is about 275.3743485824.

The spelling of 20881921 in words is "twenty million, eight hundred eighty-one thousand, nine hundred twenty-one".