21887 has 4 divisors (see below), whose sum is σ = 22440. Its totient is φ = 21336.

The previous prime is 21881. The next prime is 21893. The reversal of 21887 is 78812.

It is a semiprime because it is the product of two primes.

It is an interprime number because it is at equal distance from previous prime (21881) and next prime (21893).

It is a cyclic number.

It is not a de Polignac number, because 21887 - 2⁴ = 21871 is a prime.

It is a super-3 number, since 3×21887³ = 31454295933309, which contains 333 as substring.

It is an Ulam number.

It is a Duffinian number.

It is a plaindrome in base 4 and base 16.

It is a zygodrome in base 4.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21881) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 212 + ... + 297.

It is an arithmetic number, because the mean of its divisors is an integer number (5610).

2²¹⁸⁸⁷ is an apocalyptic number.

21887 is a deficient number, since it is larger than the sum of its proper divisors (553).

21887 is an equidigital number, since it uses as much as digits as its factorization.

21887 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 552.

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

The square root of 21887 is about 147.9425564197. The cubic root of 21887 is about 27.9723366238.

The spelling of 21887 in words is "twenty-one thousand, eight hundred eighty-seven".