21877 has 4 divisors (see below), whose sum is σ = 22176. Its totient is φ = 21580.

The previous prime is 21871. The next prime is 21881. The reversal of 21877 is 77812.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21877 is a prime.

It is a Duffinian number.

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 polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 48 + ... + 214.

It is an arithmetic number, because the mean of its divisors is an integer number (5544).

2²¹⁸⁷⁷ is an apocalyptic number.

It is an amenable number.

21877 is a deficient number, since it is larger than the sum of its proper divisors (299).

21877 is a wasteful number, since it uses less digits than its factorization.

21877 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 298.

The product of its digits is 784, while the sum is 25.

The square root of 21877 is about 147.9087556570. The cubic root of 21877 is about 27.9680758605.

It can be divided in two parts, 21 and 877, that added together give a palindrome (898).

The spelling of 21877 in words is "twenty-one thousand, eight hundred seventy-seven".