21872 has 10 divisors (see below), whose sum is σ = 42408. Its totient is φ = 10928.

The previous prime is 21871. The next prime is 21881. The reversal of 21872 is 27812.

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 (21871) by changing a digit.

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 as a sum of consecutive naturals, namely, 668 + ... + 699.

2²¹⁸⁷² is an apocalyptic number.

It is an amenable number.

21872 is a deficient number, since it is larger than the sum of its proper divisors (20536).

21872 is a wasteful number, since it uses less digits than its factorization.

21872 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1375 (or 1369 counting only the distinct ones).

The product of its digits is 224, while the sum is 20.

The square root of 21872 is about 147.8918523787. The cubic root of 21872 is about 27.9659449919.

The spelling of 21872 in words is "twenty-one thousand, eight hundred seventy-two".