21637 has 8 divisors (see below), whose sum is σ = 27072. Its totient is φ = 16800.

The previous prime is 21617. The next prime is 21647. The reversal of 21637 is 73612.

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

It is a de Polignac number, because none of the positive numbers 2^k-21637 is a prime.

It is a Duffinian number.

It is a partition number, being equal to the number of ways a set of 37 identical objects can be partitioned into subset.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21617) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 64 + ... + 217.

It is an arithmetic number, because the mean of its divisors is an integer number (3384).

2²¹⁶³⁷ is an apocalyptic number.

It is an amenable number.

21637 is a deficient number, since it is larger than the sum of its proper divisors (5435).

21637 is a wasteful number, since it uses less digits than its factorization.

21637 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 299.

The product of its digits is 252, while the sum is 19.

The square root of 21637 is about 147.0952072639. The cubic root of 21637 is about 27.8654256701.

It can be divided in two parts, 216 and 37, that added together give a triangular number (253 = T₂₂).

The spelling of 21637 in words is "twenty-one thousand, six hundred thirty-seven".