21665716 has 12 divisors (see below), whose sum is σ = 38251332. Its totient is φ = 10736768.

The previous prime is 21665713. The next prime is 21665717. The reversal of 21665716 is 61756612.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 4410000 + 17255716 = 2100^2 + 4154^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21665713) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 23515 + ... + 24418.

It is an arithmetic number, because the mean of its divisors is an integer number (3187611).

Almost surely, 2^21665716 is an apocalyptic number.

It is an amenable number.

21665716 is a deficient number, since it is larger than the sum of its proper divisors (16585616).

21665716 is a wasteful number, since it uses less digits than its factorization.

21665716 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 48050 (or 48048 counting only the distinct ones).

The product of its digits is 15120, while the sum is 34.

The square root of 21665716 is about 4654.6445621551. The cubic root of 21665716 is about 278.7774761604. Note that the first 3 decimals are identical.

The spelling of 21665716 in words is "twenty-one million, six hundred sixty-five thousand, seven hundred sixteen".