18908721 has 20 divisors (see below), whose sum is σ = 30420852. Its totient is φ = 11635488.

The previous prime is 18908717. The next prime is 18908723. The reversal of 18908721 is 12780981.

It can be written as a sum of positive squares in 2 ways, for example, as 12960000 + 5948721 = 3600^2 + 2439^2 .

It is not a de Polignac number, because 18908721 - 2² = 18908717 is a prime.

It is a hoax number, since the sum of its digits (36) coincides with the sum of the digits of its distinct prime factors.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (18908723) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 7926 + ... + 10031.

Almost surely, 2^18908721 is an apocalyptic number.

It is an amenable number.

18908721 is a deficient number, since it is larger than the sum of its proper divisors (11512131).

18908721 is a wasteful number, since it uses less digits than its factorization.

18908721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 17982 (or 17973 counting only the distinct ones).

The product of its (nonzero) digits is 8064, while the sum is 36.

The square root of 18908721 is about 4348.4159184696. The cubic root of 18908721 is about 266.4121646503.

The spelling of 18908721 in words is "eighteen million, nine hundred eight thousand, seven hundred twenty-one".