20981921 has 4 divisors (see below), whose sum is σ = 21295152. Its totient is φ = 20668692.

The previous prime is 20981899. The next prime is 20981929. The reversal of 20981921 is 12918902.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 20981921 - 2¹⁴ = 20965537 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (20981929) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 156515 + ... + 156648.

It is an arithmetic number, because the mean of its divisors is an integer number (5323788).

Almost surely, 2^20981921 is an apocalyptic number.

It is an amenable number.

20981921 is a deficient number, since it is larger than the sum of its proper divisors (313231).

20981921 is an equidigital number, since it uses as much as digits as its factorization.

20981921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 313230.

The product of its (nonzero) digits is 2592, while the sum is 32.

The square root of 20981921 is about 4580.6026896032. The cubic root of 20981921 is about 275.8132225419.

The spelling of 20981921 in words is "twenty million, nine hundred eighty-one thousand, nine hundred twenty-one".