21666607 has 4 divisors (see below), whose sum is σ = 21712320. Its totient is φ = 21620896.

The previous prime is 21666587. The next prime is 21666611. The reversal of 21666607 is 70666612.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21666607 - 2¹⁵ = 21633839 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21666637) 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, 22138 + ... + 23095.

It is an arithmetic number, because the mean of its divisors is an integer number (5428080).

Almost surely, 2^21666607 is an apocalyptic number.

21666607 is a deficient number, since it is larger than the sum of its proper divisors (45713).

21666607 is an equidigital number, since it uses as much as digits as its factorization.

21666607 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 45712.

The product of its (nonzero) digits is 18144, while the sum is 34.

The square root of 21666607 is about 4654.7402720238. The cubic root of 21666607 is about 278.7812976716.

The spelling of 21666607 in words is "twenty-one million, six hundred sixty-six thousand, six hundred seven".