21668516 has 6 divisors (see below), whose sum is σ = 37919910. Its totient is φ = 10834256.

The previous prime is 21668501. The next prime is 21668519. The reversal of 21668516 is 61586612.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 12390400 + 9278116 = 3520^2 + 3046^2 .

It is not an unprimeable number, because it can be changed into a prime (21668519) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2708561 + ... + 2708568.

It is an arithmetic number, because the mean of its divisors is an integer number (6319985).

Almost surely, 2^21668516 is an apocalyptic number.

It is an amenable number.

21668516 is a deficient number, since it is larger than the sum of its proper divisors (16251394).

21668516 is a wasteful number, since it uses less digits than its factorization.

21668516 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5417133 (or 5417131 counting only the distinct ones).

The product of its digits is 17280, while the sum is 35.

The square root of 21668516 is about 4654.9453272837. The cubic root of 21668516 is about 278.7894850459.

The spelling of 21668516 in words is "twenty-one million, six hundred sixty-eight thousand, five hundred sixteen".