21188 has 6 divisors (see below), whose sum is σ = 37086. Its totient is φ = 10592.

The previous prime is 21187. The next prime is 21191. The reversal of 21188 is 88112.

It can be written as a sum of positive squares in only one way, i.e., 20164 + 1024 = 142^2 + 32^2 .

It is an Ulam number.

It is not an unprimeable number, because it can be changed into a prime (21187) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2645 + ... + 2652.

It is an arithmetic number, because the mean of its divisors is an integer number (6181).

2²¹¹⁸⁸ is an apocalyptic number.

It is an amenable number.

21188 is a deficient number, since it is larger than the sum of its proper divisors (15898).

21188 is a wasteful number, since it uses less digits than its factorization.

21188 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5301 (or 5299 counting only the distinct ones).

The product of its digits is 128, while the sum is 20.

The square root of 21188 is about 145.5609837834. The cubic root of 21188 is about 27.6713270967.

Adding to 21188 its product of digits (128), we get a square (21316 = 146²).

The spelling of 21188 in words is "twenty-one thousand, one hundred eighty-eight".