21804421 has 4 divisors (see below), whose sum is σ = 23087052. Its totient is φ = 20521792.

The previous prime is 21804361. The next prime is 21804449. The reversal of 21804421 is 12440812.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 6320196 + 15484225 = 2514^2 + 3935^2 .

It is a cyclic number.

It is not a de Polignac number, because 21804421 - 2²³ = 13415813 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21804392 and 21804401.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21804481) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 641290 + ... + 641323.

It is an arithmetic number, because the mean of its divisors is an integer number (5771763).

Almost surely, 2^21804421 is an apocalyptic number.

It is an amenable number.

21804421 is a deficient number, since it is larger than the sum of its proper divisors (1282631).

21804421 is a wasteful number, since it uses less digits than its factorization.

21804421 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1282630.

The product of its (nonzero) digits is 512, while the sum is 22.

The square root of 21804421 is about 4669.5204250544. The cubic root of 21804421 is about 279.3711268892.

The spelling of 21804421 in words is "twenty-one million, eight hundred four thousand, four hundred twenty-one".