21919921 has 4 divisors (see below), whose sum is σ = 22247152. Its totient is φ = 21592692.

The previous prime is 21919903. The next prime is 21919927. The reversal of 21919921 is 12991912.

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 21919921 - 2²¹ = 19822769 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21919927) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 163515 + ... + 163648.

It is an arithmetic number, because the mean of its divisors is an integer number (5561788).

Almost surely, 2^21919921 is an apocalyptic number.

It is an amenable number.

21919921 is a deficient number, since it is larger than the sum of its proper divisors (327231).

21919921 is an equidigital number, since it uses as much as digits as its factorization.

21919921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 327230.

The product of its digits is 2916, while the sum is 34.

The square root of 21919921 is about 4681.8715274984. The cubic root of 21919921 is about 279.8635432030.

The spelling of 21919921 in words is "twenty-one million, nine hundred nineteen thousand, nine hundred twenty-one".