21205712 has 40 divisors (see below), whose sum is σ = 45479232. Its totient is φ = 9497600.

The previous prime is 21205703. The next prime is 21205727. The reversal of 21205712 is 21750212.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 11648 + ... + 13344.

Almost surely, 2^21205712 is an apocalyptic number.

21205712 is a gapful number since it is divisible by the number (22) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21205712, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (22739616).

21205712 is an abundant number, since it is smaller than the sum of its proper divisors (24273520).

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

21205712 is a wasteful number, since it uses less digits than its factorization.

21205712 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1787 (or 1781 counting only the distinct ones).

The product of its (nonzero) digits is 280, while the sum is 20.

The square root of 21205712 is about 4604.9660150755. The cubic root of 21205712 is about 276.7903551720.

Adding to 21205712 its reverse (21750212), we get a palindrome (42955924).

The spelling of 21205712 in words is "twenty-one million, two hundred five thousand, seven hundred twelve".