16813721 has 4 divisors (see below), whose sum is σ = 16859172. Its totient is φ = 16768272.

The previous prime is 16813691. The next prime is 16813729. The reversal of 16813721 is 12731861.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12731861 = 17 ⋅748933.

It can be written as a sum of positive squares in 2 ways, for example, as 9388096 + 7425625 = 3064^2 + 2725^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-16813721 is a prime.

It is a Duffinian number.

It is a nialpdrome in base 11.

It is not an unprimeable number, because it can be changed into a prime (16813729) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 22166 + ... + 22911.

It is an arithmetic number, because the mean of its divisors is an integer number (4214793).

Almost surely, 2^16813721 is an apocalyptic number.

It is an amenable number.

16813721 is a deficient number, since it is larger than the sum of its proper divisors (45451).

16813721 is an equidigital number, since it uses as much as digits as its factorization.

16813721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 45450.

The product of its digits is 2016, while the sum is 29.

The square root of 16813721 is about 4100.4537553788. The cubic root of 16813721 is about 256.1855395268.

It can be divided in two parts, 1681 and 3721, that multiplied together give a square (6255001 = 2501²).

The spelling of 16813721 in words is "sixteen million, eight hundred thirteen thousand, seven hundred twenty-one".