21788 has 12 divisors (see below), whose sum is σ = 41160. Its totient is φ = 10032.

The previous prime is 21787. The next prime is 21799. The reversal of 21788 is 88712.

It is a Harshad number since it is a multiple of its sum of digits (26).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21787) 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 in 3 ways as a sum of consecutive naturals, for example, 158 + ... + 261.

It is an arithmetic number, because the mean of its divisors is an integer number (3430).

2²¹⁷⁸⁸ is an apocalyptic number.

It is an amenable number.

21788 is a deficient number, since it is larger than the sum of its proper divisors (19372).

21788 is a wasteful number, since it uses less digits than its factorization.

21788 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 436 (or 434 counting only the distinct ones).

The product of its digits is 896, while the sum is 26.

The square root of 21788 is about 147.6075878808. The cubic root of 21788 is about 27.9300977424.

21788 divided by its sum of digits (26) gives a palindrome (838).

It can be divided in two parts, 2178 and 8, that multiplied together give a square (17424 = 132²).

The spelling of 21788 in words is "twenty-one thousand, seven hundred eighty-eight".