21004427 has 4 divisors (see below), whose sum is σ = 21300336. Its totient is φ = 20708520.

The previous prime is 21004387. The next prime is 21004447. The reversal of 21004427 is 72440012.

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

It is a cyclic number.

It is not a de Polignac number, because 21004427 - 2²⁰ = 19955851 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21004399 and 21004408.

It is not an unprimeable number, because it can be changed into a prime (21004447) 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, 147848 + ... + 147989.

It is an arithmetic number, because the mean of its divisors is an integer number (5325084).

Almost surely, 2^21004427 is an apocalyptic number.

21004427 is a deficient number, since it is larger than the sum of its proper divisors (295909).

21004427 is an equidigital number, since it uses as much as digits as its factorization.

21004427 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 295908.

The product of its (nonzero) digits is 448, while the sum is 20.

The square root of 21004427 is about 4583.0586948020. The cubic root of 21004427 is about 275.9118031924.

Adding to 21004427 its reverse (72440012), we get a palindrome (93444439).

The spelling of 21004427 in words is "twenty-one million, four thousand, four hundred twenty-seven".