20988921 has 4 divisors (see below), whose sum is σ = 27985232. Its totient is φ = 13992612.

The previous prime is 20988917. The next prime is 20988923. The reversal of 20988921 is 12988902.

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 not a de Polignac number, because 20988921 - 2² = 20988917 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 20988921.

It is not an unprimeable number, because it can be changed into a prime (20988923) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3498151 + ... + 3498156.

It is an arithmetic number, because the mean of its divisors is an integer number (6996308).

Almost surely, 2^20988921 is an apocalyptic number.

It is an amenable number.

20988921 is a deficient number, since it is larger than the sum of its proper divisors (6996311).

20988921 is an equidigital number, since it uses as much as digits as its factorization.

20988921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6996310.

The product of its (nonzero) digits is 20736, while the sum is 39.

The square root of 20988921 is about 4581.3667174763. The cubic root of 20988921 is about 275.8438914511.

The spelling of 20988921 in words is "twenty million, nine hundred eighty-eight thousand, nine hundred twenty-one".