21006428 has 6 divisors (see below), whose sum is σ = 36761256. Its totient is φ = 10503212.

The previous prime is 21006421. The next prime is 21006431. The reversal of 21006428 is 82460012.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21006421) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2625800 + ... + 2625807.

It is an arithmetic number, because the mean of its divisors is an integer number (6126876).

Almost surely, 2^21006428 is an apocalyptic number.

It is an amenable number.

21006428 is a deficient number, since it is larger than the sum of its proper divisors (15754828).

21006428 is a wasteful number, since it uses less digits than its factorization.

21006428 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5251611 (or 5251609 counting only the distinct ones).

The product of its (nonzero) digits is 768, while the sum is 23.

The square root of 21006428 is about 4583.2769935931. The cubic root of 21006428 is about 275.9205645515.

The spelling of 21006428 in words is "twenty-one million, six thousand, four hundred twenty-eight".