21659 has 6 divisors (see below), whose sum is σ = 23940. Its totient is φ = 19580.

The previous prime is 21649. The next prime is 21661. The reversal of 21659 is 95612.

It is a de Polignac number, because none of the positive numbers 2^k-21659 is a prime.

It is a super-2 number, since 2×21659² = 938224562, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21649) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 32 + ... + 210.

It is an arithmetic number, because the mean of its divisors is an integer number (3990).

2²¹⁶⁵⁹ is an apocalyptic number.

21659 is a deficient number, since it is larger than the sum of its proper divisors (2281).

21659 is a wasteful number, since it uses less digits than its factorization.

21659 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 201 (or 190 counting only the distinct ones).

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

The square root of 21659 is about 147.1699697629. The cubic root of 21659 is about 27.8748667773.

It can be divided in two parts, 2 and 1659, that added together give a palindrome (1661).

The spelling of 21659 in words is "twenty-one thousand, six hundred fifty-nine".