21072 has 20 divisors (see below), whose sum is σ = 54560. Its totient is φ = 7008.

The previous prime is 21067. The next prime is 21089. The reversal of 21072 is 27012.

21072 is nontrivially palindromic in base 9.

It is a Harshad number since it is a multiple of its sum of digits (12).

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

It is a congruent number.

It is an unprimeable number.

21072 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 (5) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 172 + ... + 267.

It is an arithmetic number, because the mean of its divisors is an integer number (2728).

2²¹⁰⁷² is an apocalyptic number.

It is an amenable number.

21072 is an abundant number, since it is smaller than the sum of its proper divisors (33488).

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 (27280).

21072 is a wasteful number, since it uses less digits than its factorization.

21072 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 450 (or 444 counting only the distinct ones).

The product of its (nonzero) digits is 28, while the sum is 12.

The square root of 21072 is about 145.1619784930. The cubic root of 21072 is about 27.6207363594.

Adding to 21072 its reverse (27012), we get a palindrome (48084).

It can be divided in two parts, 210 and 72, that added together give a palindrome (282).

The spelling of 21072 in words is "twenty-one thousand, seventy-two", and thus it is an iban number.