18751721 has 4 divisors (see below), whose sum is σ = 18821700. Its totient is φ = 18681744.

The previous prime is 18751717. The next prime is 18751723. The reversal of 18751721 is 12715781.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 570025 + 18181696 = 755^2 + 4264^2 .

It is a cyclic number.

It is not a de Polignac number, because 18751721 - 2² = 18751717 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (18751723) 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 3 ways as a sum of consecutive naturals, for example, 34586 + ... + 35123.

It is an arithmetic number, because the mean of its divisors is an integer number (4705425).

Almost surely, 2^18751721 is an apocalyptic number.

It is an amenable number.

18751721 is a deficient number, since it is larger than the sum of its proper divisors (69979).

18751721 is an equidigital number, since it uses as much as digits as its factorization.

18751721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 69978.

The product of its digits is 3920, while the sum is 32.

The square root of 18751721 is about 4330.3257383250. The cubic root of 18751721 is about 265.6727702043.

The spelling of 18751721 in words is "eighteen million, seven hundred fifty-one thousand, seven hundred twenty-one".