18291721 has 8 divisors (see below), whose sum is σ = 21625920. Its totient is φ = 15137808.

The previous prime is 18291719. The next prime is 18291733. The reversal of 18291721 is 12719281.

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

It is not a de Polignac number, because 18291721 - 2¹ = 18291719 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (18291701) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 44851 + ... + 45256.

It is an arithmetic number, because the mean of its divisors is an integer number (2703240).

Almost surely, 2^18291721 is an apocalyptic number.

It is an amenable number.

18291721 is a deficient number, since it is larger than the sum of its proper divisors (3334199).

18291721 is an equidigital number, since it uses as much as digits as its factorization.

18291721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 90143.

The product of its digits is 2016, while the sum is 31.

The square root of 18291721 is about 4276.8821587694. The cubic root of 18291721 is about 263.4823467176.

The spelling of 18291721 in words is "eighteen million, two hundred ninety-one thousand, seven hundred twenty-one".