21672 has 48 divisors (see below), whose sum is σ = 68640. Its totient is φ = 6048.

The previous prime is 21661. The next prime is 21673. The reversal of 21672 is 27612.

Added to its reverse (27612) it gives a square (49284 = 222²).

It is a happy number.

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

It is a nude number because it is divisible by every one of its digits and also a Zuckerman number because it is divisible by the product of its digits.

It is an alternating number because its digits alternate between even and odd.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21673) by changing a digit.

21672 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, 483 + ... + 525.

It is an arithmetic number, because the mean of its divisors is an integer number (1430).

2²¹⁶⁷² is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21672, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34320).

21672 is an abundant number, since it is smaller than the sum of its proper divisors (46968).

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

21672 is a wasteful number, since it uses less digits than its factorization.

21672 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 62 (or 55 counting only the distinct ones).

The product of its digits is 168, while the sum is 18.

The square root of 21672 is about 147.2141297566. The cubic root of 21672 is about 27.8804426086.

Adding to 21672 its reverse (27612), we get a square (49284 = 222²).

It can be divided in two parts, 2167 and 2, that multiplied together give a palindrome (4334).

The spelling of 21672 in words is "twenty-one thousand, six hundred seventy-two".