21967 has 4 divisors (see below), whose sum is σ = 23976. Its totient is φ = 19960.

The previous prime is 21961. The next prime is 21977. The reversal of 21967 is 76912.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21967 - 2⁷ = 21839 is a prime.

It is a Duffinian number.

21967 is a lucky 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 (21961) 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, 988 + ... + 1009.

It is an arithmetic number, because the mean of its divisors is an integer number (5994).

2²¹⁹⁶⁷ is an apocalyptic number.

21967 is a deficient number, since it is larger than the sum of its proper divisors (2009).

21967 is a wasteful number, since it uses less digits than its factorization.

21967 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2008.

The product of its digits is 756, while the sum is 25.

The square root of 21967 is about 148.2126850172. The cubic root of 21967 is about 28.0063760990.

Subtracting 21967 from its reverse (76912), we obtain a palindrome (54945).

The spelling of 21967 in words is "twenty-one thousand, nine hundred sixty-seven".