21942 has 24 divisors (see below), whose sum is σ = 50544. Its totient is φ = 6864.

The previous prime is 21937. The next prime is 21943. The reversal of 21942 is 24912.

It is a hoax number, since the sum of its digits (18) coincides with the sum of the digits of its distinct prime factors.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a plaindrome in base 15.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21943) by changing a digit.

21942 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 388 + ... + 440.

It is an arithmetic number, because the mean of its divisors is an integer number (2106).

2²¹⁹⁴² is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21942, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25272).

21942 is an abundant number, since it is smaller than the sum of its proper divisors (28602).

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

21942 is a wasteful number, since it uses less digits than its factorization.

21942 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 84 (or 81 counting only the distinct ones).

The product of its digits is 144, while the sum is 18.

The square root of 21942 is about 148.1283227475. The cubic root of 21942 is about 27.9957476536.

The spelling of 21942 in words is "twenty-one thousand, nine hundred forty-two".