21869 has 4 divisors (see below), whose sum is σ = 23040. Its totient is φ = 20700.

The previous prime is 21863. The next prime is 21871. The reversal of 21869 is 96812.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21869 - 2⁸ = 21613 is a prime.

It is a super-2 number, since 2×21869² = 956506322, which contains 22 as substring.

It is a Duffinian number.

It is a plaindrome in base 16.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21863) 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, 557 + ... + 594.

It is an arithmetic number, because the mean of its divisors is an integer number (5760).

2²¹⁸⁶⁹ is an apocalyptic number.

It is an amenable number.

21869 is a deficient number, since it is larger than the sum of its proper divisors (1171).

21869 is a wasteful number, since it uses less digits than its factorization.

21869 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1170.

The product of its digits is 864, while the sum is 26.

The square root of 21869 is about 147.8817094843. The cubic root of 21869 is about 27.9646663149.

The spelling of 21869 in words is "twenty-one thousand, eight hundred sixty-nine".