21682 has 8 divisors (see below), whose sum is σ = 33516. Its totient is φ = 10512.

The previous prime is 21673. The next prime is 21683. The reversal of 21682 is 28612.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 16641 + 5041 = 129^2 + 71^2 .

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

It is not an unprimeable number, because it can be changed into a prime (21683) by changing a digit.

21682 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

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, 73 + ... + 220.

2²¹⁶⁸² is an apocalyptic number.

21682 is the 74-th decagonal number.

21682 is a deficient number, since it is larger than the sum of its proper divisors (11834).

21682 is a wasteful number, since it uses less digits than its factorization.

21682 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 332.

The product of its digits is 192, while the sum is 19.

The square root of 21682 is about 147.2480899706. The cubic root of 21682 is about 27.8847301925.

It can be divided in two parts, 21 and 682, that added together give a triangular number (703 = T₃₇).

The spelling of 21682 in words is "twenty-one thousand, six hundred eighty-two".