21758 has 16 divisors (see below), whose sum is σ = 38016. Its totient is φ = 9240.

The previous prime is 21757. The next prime is 21767. The reversal of 21758 is 85712.

It is a Harshad number since it is a multiple of its sum of digits (23).

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21751) 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, 485 + ... + 527.

It is an arithmetic number, because the mean of its divisors is an integer number (2376).

2²¹⁷⁵⁸ is an apocalyptic number.

21758 is a deficient number, since it is larger than the sum of its proper divisors (16258).

21758 is a wasteful number, since it uses less digits than its factorization.

21758 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 79.

The product of its digits is 560, while the sum is 23.

The square root of 21758 is about 147.5059320841. The cubic root of 21758 is about 27.9172728266.

21758 divided by its sum of digits (23) gives a triangular number (946 = T₄₃).

The spelling of 21758 in words is "twenty-one thousand, seven hundred fifty-eight".