21205206 has 64 divisors (see below), whose sum is σ = 53222400. Its totient is φ = 6199200.

The previous prime is 21205183. The next prime is 21205207. The reversal of 21205206 is 60250212.

It is a super-3 number, since 3×21205206³ (a number of 23 digits) contains 333 as substring.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21205207) 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 31 ways as a sum of consecutive naturals, for example, 16611 + ... + 17841.

It is an arithmetic number, because the mean of its divisors is an integer number (831600).

Almost surely, 2^21205206 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21205206, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26611200).

21205206 is an abundant number, since it is smaller than the sum of its proper divisors (32017194).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21205206 is a wasteful number, since it uses less digits than its factorization.

21205206 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1282 (or 1276 counting only the distinct ones).

The product of its (nonzero) digits is 240, while the sum is 18.

The square root of 21205206 is about 4604.9110740600. The cubic root of 21205206 is about 276.7881536105.

Adding to 21205206 its reverse (60250212), we get a palindrome (81455418).

The spelling of 21205206 in words is "twenty-one million, two hundred five thousand, two hundred six".