21004406 has 4 divisors (see below), whose sum is σ = 31506612. Its totient is φ = 10502202.

The previous prime is 21004387. The next prime is 21004447. The reversal of 21004406 is 60440012.

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

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5251100 + ... + 5251103.

It is an arithmetic number, because the mean of its divisors is an integer number (7876653).

Almost surely, 2^21004406 is an apocalyptic number.

21004406 is a deficient number, since it is larger than the sum of its proper divisors (10502206).

21004406 is a wasteful number, since it uses less digits than its factorization.

21004406 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10502205.

The product of its (nonzero) digits is 192, while the sum is 17.

The square root of 21004406 is about 4583.0564037550. The cubic root of 21004406 is about 275.9117112411.

Adding to 21004406 its reverse (60440012), we get a palindrome (81444418).

The spelling of 21004406 in words is "twenty-one million, four thousand, four hundred six".