21009828 has 36 divisors (see below), whose sum is σ = 57028272. Its totient is φ = 6002640.

The previous prime is 21009827. The next prime is 21009851. The reversal of 21009828 is 82890012.

It is a junction number, because it is equal to n+sod(n) for n = 21009795 and 21009804.

It is not an unprimeable number, because it can be changed into a prime (21009827) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 17278 + ... + 18453.

Almost surely, 2^21009828 is an apocalyptic number.

21009828 is a gapful number since it is divisible by the number (28) formed by its first and last digit.

It is an amenable number.

21009828 is an abundant number, since it is smaller than the sum of its proper divisors (36018444).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21009828 is a wasteful number, since it uses less digits than its factorization.

21009828 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 35752 (or 35743 counting only the distinct ones).

The product of its (nonzero) digits is 2304, while the sum is 30.

The square root of 21009828 is about 4583.6478922361. The cubic root of 21009828 is about 275.9354501429.

The spelling of 21009828 in words is "twenty-one million, nine thousand, eight hundred twenty-eight".