21646 has 8 divisors (see below), whose sum is σ = 33120. Its totient is φ = 10608.

The previous prime is 21617. The next prime is 21647. The reversal of 21646 is 64612.

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

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 (21647) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 90 + ... + 226.

It is an arithmetic number, because the mean of its divisors is an integer number (4140).

2²¹⁶⁴⁶ is an apocalyptic number.

21646 is the 79-th nonagonal number.

21646 is a deficient number, since it is larger than the sum of its proper divisors (11474).

21646 is a wasteful number, since it uses less digits than its factorization.

21646 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 218.

The product of its digits is 288, while the sum is 19.

The square root of 21646 is about 147.1257965144. The cubic root of 21646 is about 27.8692887144.

It can be divided in two parts, 216 and 46, that added together give a palindrome (262).

The spelling of 21646 in words is "twenty-one thousand, six hundred forty-six".