21205716 has 24 divisors (see below), whose sum is σ = 56548800. Its totient is φ = 6058752.

The previous prime is 21205703. The next prime is 21205727. The reversal of 21205716 is 61750212.

It is a congruent number.

It is an unprimeable number.

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 7 ways as a sum of consecutive naturals, for example, 126141 + ... + 126308.

It is an arithmetic number, because the mean of its divisors is an integer number (2356200).

Almost surely, 2^21205716 is an apocalyptic number.

It is an amenable number.

21205716 is an abundant number, since it is smaller than the sum of its proper divisors (35343084).

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

21205716 is a wasteful number, since it uses less digits than its factorization.

21205716 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 252463 (or 252461 counting only the distinct ones).

The product of its (nonzero) digits is 840, while the sum is 24.

The square root of 21205716 is about 4604.9664493892. The cubic root of 21205716 is about 276.7903725755.

Adding to 21205716 its reverse (61750212), we get a palindrome (82955928).

The spelling of 21205716 in words is "twenty-one million, two hundred five thousand, seven hundred sixteen".