21028403 has 4 divisors (see below), whose sum is σ = 22940088. Its totient is φ = 19116720.

The previous prime is 21028391. The next prime is 21028409. The reversal of 21028403 is 30482012.

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 21028403 - 2⁴ = 21028387 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21028409) 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, 955826 + ... + 955847.

It is an arithmetic number, because the mean of its divisors is an integer number (5735022).

Almost surely, 2^21028403 is an apocalyptic number.

21028403 is a deficient number, since it is larger than the sum of its proper divisors (1911685).

21028403 is a wasteful number, since it uses less digits than its factorization.

21028403 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1911684.

The product of its (nonzero) digits is 384, while the sum is 20.

The square root of 21028403 is about 4585.6736691570. The cubic root of 21028403 is about 276.0167452908.

The spelling of 21028403 in words is "twenty-one million, twenty-eight thousand, four hundred three".