21087 has 16 divisors (see below), whose sum is σ = 34560. Its totient is φ = 12600.

The previous prime is 21067. The next prime is 21089. The reversal of 21087 is 78012.

It is not a de Polignac number, because 21087 - 2⁶ = 21023 is a prime.

It is a zygodrome in base 5.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 21087.

It is not an unprimeable number, because it can be changed into a prime (21089) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 262 + ... + 332.

It is an arithmetic number, because the mean of its divisors is an integer number (2160).

2²¹⁰⁸⁷ is an apocalyptic number.

21087 is a gapful number since it is divisible by the number (27) formed by its first and last digit.

21087 is a deficient number, since it is larger than the sum of its proper divisors (13473).

21087 is a wasteful number, since it uses less digits than its factorization.

21087 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 91 (or 85 counting only the distinct ones).

The product of its (nonzero) digits is 112, while the sum is 18.

The square root of 21087 is about 145.2136357234. The cubic root of 21087 is about 27.6272887002.

Adding to 21087 its reverse (78012), we get a palindrome (99099).

It can be divided in two parts, 2 and 1087, that added together give a square (1089 = 33²).

The spelling of 21087 in words is "twenty-one thousand, eighty-seven".