21638 has 8 divisors (see below), whose sum is σ = 33600. Its totient is φ = 10440.

The previous prime is 21617. The next prime is 21647. The reversal of 21638 is 83612.

It is a sphenic number, since it is the product of 3 distinct primes.

It is an alternating number because its digits alternate between even and odd.

It is a congruent number.

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, 113 + ... + 236.

It is an arithmetic number, because the mean of its divisors is an integer number (4200).

2²¹⁶³⁸ is an apocalyptic number.

21638 is a deficient number, since it is larger than the sum of its proper divisors (11962).

21638 is a wasteful number, since it uses less digits than its factorization.

21638 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 382.

The product of its digits is 288, while the sum is 20.

The square root of 21638 is about 147.0986063836. The cubic root of 21638 is about 27.8658549502.

The spelling of 21638 in words is "twenty-one thousand, six hundred thirty-eight".