21790 has 8 divisors (see below), whose sum is σ = 39240. Its totient is φ = 8712.

The previous prime is 21787. The next prime is 21799. The reversal of 21790 is 9712.

21790 = 23² + 24² + ... + 42².

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21799) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1080 + ... + 1099.

It is an arithmetic number, because the mean of its divisors is an integer number (4905).

2²¹⁷⁹⁰ is an apocalyptic number.

21790 is a deficient number, since it is larger than the sum of its proper divisors (17450).

21790 is a wasteful number, since it uses less digits than its factorization.

21790 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2186.

The product of its (nonzero) digits is 126, while the sum is 19.

The square root of 21790 is about 147.6143624449. The cubic root of 21790 is about 27.9309523181.

The spelling of 21790 in words is "twenty-one thousand, seven hundred ninety".