21738 has 8 divisors (see below), whose sum is σ = 43488. Its totient is φ = 7244.

The previous prime is 21737. The next prime is 21739. The reversal of 21738 is 83712.

It is an interprime number because it is at equal distance from previous prime (21737) and next prime (21739).

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

21738 is an admirable number.

It is an Ulam number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21737) 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, 1806 + ... + 1817.

It is an arithmetic number, because the mean of its divisors is an integer number (5436).

2²¹⁷³⁸ is an apocalyptic number.

21738 is a primitive abundant number, since it is smaller than the sum of its proper divisors, none of which is abundant.

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

It is a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (21744).

21738 is a wasteful number, since it uses less digits than its factorization.

21738 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3628.

The product of its digits is 336, while the sum is 21.

The square root of 21738 is about 147.4381226142. The cubic root of 21738 is about 27.9087163321.

The spelling of 21738 in words is "twenty-one thousand, seven hundred thirty-eight".