21965 has 8 divisors (see below), whose sum is σ = 27648. Its totient is φ = 16720.

The previous prime is 21961. The next prime is 21977. The reversal of 21965 is 56912.

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

It is not a de Polignac number, because 21965 - 2² = 21961 is a prime.

It is a super-2 number, since 2×21965² = 964922450, which contains 22 as substring.

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

It is a Duffinian number.

It is a plaindrome in base 11 and base 16.

It is a self number, because there is not a number n which added to its sum of digits gives 21965.

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 7 ways as a sum of consecutive naturals, for example, 20 + ... + 210.

It is an arithmetic number, because the mean of its divisors is an integer number (3456).

2²¹⁹⁶⁵ is an apocalyptic number.

It is an amenable number.

21965 is a deficient number, since it is larger than the sum of its proper divisors (5683).

21965 is a wasteful number, since it uses less digits than its factorization.

21965 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 219.

The product of its digits is 540, while the sum is 23.

The square root of 21965 is about 148.2059378028. The cubic root of 21965 is about 28.0055261202.

The spelling of 21965 in words is "twenty-one thousand, nine hundred sixty-five".