21693 has 8 divisors (see below), whose sum is σ = 33088. Its totient is φ = 12384.

The previous prime is 21683. The next prime is 21701. The reversal of 21693 is 39612.

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

It is not a de Polignac number, because 21693 - 2⁵ = 21661 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (21), and also a Moran number because the ratio is a prime number: 1033 = 21693 / (2 + 1 + 6 + 9 + 3).

It is a Duffinian number.

21693 is a lucky number.

It is a nialpdrome in base 15.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21613) 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, 496 + ... + 537.

It is an arithmetic number, because the mean of its divisors is an integer number (4136).

2²¹⁶⁹³ is an apocalyptic number.

It is an amenable number.

21693 is a deficient number, since it is larger than the sum of its proper divisors (11395).

21693 is a wasteful number, since it uses less digits than its factorization.

21693 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1043.

The product of its digits is 324, while the sum is 21.

The square root of 21693 is about 147.2854371620. The cubic root of 21693 is about 27.8894450124.

The spelling of 21693 in words is "twenty-one thousand, six hundred ninety-three".