18666721 has 8 divisors (see below), whose sum is σ = 19710080. Its totient is φ = 17629488.

The previous prime is 18666709. The next prime is 18666733. The reversal of 18666721 is 12766681.

It is an interprime number because it is at equal distance from previous prime (18666709) and next prime (18666733).

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

It is a cyclic number.

It is not a de Polignac number, because 18666721 - 2¹¹ = 18664673 is a prime.

It is the 4321-st Hogben number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (18666761) by changing a digit.

It is a nontrivial repunit in base 4320.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 5635 + ... + 8311.

It is an arithmetic number, because the mean of its divisors is an integer number (2463760).

Almost surely, 2^18666721 is an apocalyptic number.

It is an amenable number.

18666721 is a deficient number, since it is larger than the sum of its proper divisors (1043359).

18666721 is a wasteful number, since it uses less digits than its factorization.

18666721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3063.

The product of its digits is 24192, while the sum is 37.

The square root of 18666721 is about 4320.5000867955. The cubic root of 18666721 is about 265.2707379017.

The spelling of 18666721 in words is "eighteen million, six hundred sixty-six thousand, seven hundred twenty-one".