21307666 has 8 divisors (see below), whose sum is σ = 32485644. Its totient is φ = 10479120.

The previous prime is 21307609. The next prime is 21307669. The reversal of 21307666 is 66670312.

It can be written as a sum of positive squares in 2 ways, for example, as 12752041 + 8555625 = 3571^2 + 2925^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is not an unprimeable number, because it can be changed into a prime (21307669) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 87205 + ... + 87448.

Almost surely, 2^21307666 is an apocalyptic number.

21307666 is a deficient number, since it is larger than the sum of its proper divisors (11177978).

21307666 is a wasteful number, since it uses less digits than its factorization.

21307666 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 174716.

The product of its (nonzero) digits is 9072, while the sum is 31.

The square root of 21307666 is about 4616.0227469110. The cubic root of 21307666 is about 277.2332355081.

Adding to 21307666 its reverse (66670312), we get a palindrome (87977978).

The spelling of 21307666 in words is "twenty-one million, three hundred seven thousand, six hundred sixty-six".