21550 has 12 divisors (see below), whose sum is σ = 40176. Its totient is φ = 8600.

The previous prime is 21529. The next prime is 21557. The reversal of 21550 is 5512.

It is a self number, because there is not a number n which added to its sum of digits gives 21550.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21557) 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 5 ways as a sum of consecutive naturals, for example, 166 + ... + 265.

It is an arithmetic number, because the mean of its divisors is an integer number (3348).

2²¹⁵⁵⁰ is an apocalyptic number.

21550 is a deficient number, since it is larger than the sum of its proper divisors (18626).

21550 is a wasteful number, since it uses less digits than its factorization.

21550 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 443 (or 438 counting only the distinct ones).

The product of its (nonzero) digits is 50, while the sum is 13.

The square root of 21550 is about 146.7991825590. The cubic root of 21550 is about 27.8280275622.

The spelling of 21550 in words is "twenty-one thousand, five hundred fifty".