18871813 has 4 divisors (see below), whose sum is σ = 19381900. Its totient is φ = 18361728.

The previous prime is 18871789. The next prime is 18871841. The reversal of 18871813 is 31817881.

It is the 1774-th star number.

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 13410244 + 5461569 = 3662^2 + 2337^2 .

It is a cyclic number.

It is not a de Polignac number, because 18871813 - 2⁵ = 18871781 is a prime.

It is a super-2 number, since 2×18871813² = 712290651813938, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (37), and also a Moran number because the ratio is a prime number: 510049 = 18871813 / (1 + 8 + 8 + 7 + 1 + 8 + 1 + 3).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18871873) 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, 254988 + ... + 255061.

It is an arithmetic number, because the mean of its divisors is an integer number (4845475).

Almost surely, 2^18871813 is an apocalyptic number.

It is an amenable number.

18871813 is a deficient number, since it is larger than the sum of its proper divisors (510087).

18871813 is an equidigital number, since it uses as much as digits as its factorization.

18871813 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 510086.

The product of its digits is 10752, while the sum is 37.

The square root of 18871813 is about 4344.1700012776. The cubic root of 18871813 is about 266.2387147972.

The spelling of 18871813 in words is "eighteen million, eight hundred seventy-one thousand, eight hundred thirteen".