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 2k-21877 is a prime.
It is a Duffinian number.
It is a congruent number.
221877 is an apocalyptic number.
It is an amenable number.
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 square root of 21877 is about 147.9087556570. The cubic root of 21877 is about 27.9680758605.
The spelling of 21877 in words is "twenty-one thousand, eight hundred seventy-seven".