21213828 has 18 divisors (see below), whose sum is σ = 53623934. Its totient is φ = 7071264.

The previous prime is 21213811. The next prime is 21213847. The reversal of 21213828 is 82831212.

It can be written as a sum of positive squares in only one way, i.e., 19342404 + 1871424 = 4398^2 + 1368^2 .

It is a tau number, because it is divible by the number of its divisors (18).

It is an unprimeable number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 294601 + ... + 294672.

Almost surely, 2^21213828 is an apocalyptic number.

It is an amenable number.

21213828 is an abundant number, since it is smaller than the sum of its proper divisors (32410106).

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

21213828 is a wasteful number, since it uses less digits than its factorization.

21213828 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 589283 (or 589278 counting only the distinct ones).

The product of its digits is 1536, while the sum is 27.

The square root of 21213828 is about 4605.8471533476. The cubic root of 21213828 is about 276.8256623885.

The spelling of 21213828 in words is "twenty-one million, two hundred thirteen thousand, eight hundred twenty-eight".