21660018 has 8 divisors (see below), whose sum is σ = 43320048. Its totient is φ = 7220004.

The previous prime is 21660011. The next prime is 21660047. The reversal of 21660018 is 81006612.

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

21660018 is an admirable number.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21660018.

It is not an unprimeable number, because it can be changed into a prime (21660011) 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, 1804996 + ... + 1805007.

It is an arithmetic number, because the mean of its divisors is an integer number (5415006).

Almost surely, 2^21660018 is an apocalyptic number.

21660018 is a primitive abundant number, since it is smaller than the sum of its proper divisors, none of which is abundant.

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

21660018 is a wasteful number, since it uses less digits than its factorization.

21660018 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3610008.

The product of its (nonzero) digits is 576, while the sum is 24.

The square root of 21660018 is about 4654.0324450953. The cubic root of 21660018 is about 278.7530348829.

The spelling of 21660018 in words is "twenty-one million, six hundred sixty thousand, eighteen".