21000028 has 36 divisors (see below), whose sum is σ = 43012200. Its totient is φ = 8944992.

The previous prime is 20999999. The next prime is 21000037. The reversal of 21000028 is 82000012.

It is a junction number, because it is equal to n+sod(n) for n = 20999981 and 21000017.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 59998 + ... + 60346.

Almost surely, 2^21000028 is an apocalyptic number.

21000028 is a gapful number since it is divisible by the number (28) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21000028, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (21506100).

21000028 is an abundant number, since it is smaller than the sum of its proper divisors (22012172).

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

21000028 is a wasteful number, since it uses less digits than its factorization.

21000028 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 674 (or 665 counting only the distinct ones).

The product of its (nonzero) digits is 32, while the sum is 13.

The square root of 21000028 is about 4582.5787500053. The cubic root of 21000028 is about 275.8925402569.

The spelling of 21000028 in words is "twenty-one million, twenty-eight", and thus it is an aban number and an uban number.