21628 has 6 divisors (see below), whose sum is σ = 37856. Its totient is φ = 10812.

The previous prime is 21617. The next prime is 21647. The reversal of 21628 is 82612.

It is a happy number.

It is an Ulam number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2700 + ... + 2707.

2²¹⁶²⁸ is an apocalyptic number.

It is an amenable number.

21628 is a deficient number, since it is larger than the sum of its proper divisors (16228).

21628 is a wasteful number, since it uses less digits than its factorization.

21628 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5411 (or 5409 counting only the distinct ones).

The product of its digits is 192, while the sum is 19.

The square root of 21628 is about 147.0646116508. The cubic root of 21628 is about 27.8615615545.

Subtracting from 21628 its sum of digits (19), we obtain a square (21609 = 147²).

The spelling of 21628 in words is "twenty-one thousand, six hundred twenty-eight".