21621228 has 12 divisors (see below), whose sum is σ = 50449560. Its totient is φ = 7207072.

The previous prime is 21621181. The next prime is 21621233. The reversal of 21621228 is 82212612.

It is a tau number, because it is divible by the number of its divisors (12).

It is a junction number, because it is equal to n+sod(n) for n = 21621198 and 21621207.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 900873 + ... + 900896.

It is an arithmetic number, because the mean of its divisors is an integer number (4204130).

Almost surely, 2^21621228 is an apocalyptic number.

It is an amenable number.

21621228 is an abundant number, since it is smaller than the sum of its proper divisors (28828332).

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

21621228 is a wasteful number, since it uses less digits than its factorization.

21621228 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1801776 (or 1801774 counting only the distinct ones).

The product of its digits is 768, while the sum is 24.

The square root of 21621228 is about 4649.8632237949. The cubic root of 21621228 is about 278.5865331530.

The spelling of 21621228 in words is "twenty-one million, six hundred twenty-one thousand, two hundred twenty-eight".