18117721 has 12 divisors (see below), whose sum is σ = 19609380. Its totient is φ = 16718240.

The previous prime is 18117719. The next prime is 18117727. The reversal of 18117721 is 12771181.

It can be written as a sum of positive squares in 2 ways, for example, as 13542400 + 4575321 = 3680^2 + 2139^2 .

It is not a de Polignac number, because 18117721 - 2¹ = 18117719 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 18117721.

It is not an unprimeable number, because it can be changed into a prime (18117727) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 14751 + ... + 15931.

It is an arithmetic number, because the mean of its divisors is an integer number (1634115).

Almost surely, 2^18117721 is an apocalyptic number.

It is an amenable number.

18117721 is a deficient number, since it is larger than the sum of its proper divisors (1491659).

18117721 is a wasteful number, since it uses less digits than its factorization.

18117721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1256 (or 1233 counting only the distinct ones).

The product of its digits is 784, while the sum is 28.

The square root of 18117721 is about 4256.4916304393. The cubic root of 18117721 is about 262.6442249015.

The spelling of 18117721 in words is "eighteen million, one hundred seventeen thousand, seven hundred twenty-one".