18617821 has 4 divisors (see below), whose sum is σ = 18827100. Its totient is φ = 18408544.

The previous prime is 18617791. The next prime is 18617827. The reversal of 18617821 is 12871681.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12871681 = 191 ⋅67391.

It can be written as a sum of positive squares in 2 ways, for example, as 3290596 + 15327225 = 1814^2 + 3915^2 .

It is a cyclic number.

It is not a de Polignac number, because 18617821 - 2¹⁹ = 18093533 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18617827) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 104506 + ... + 104683.

It is an arithmetic number, because the mean of its divisors is an integer number (4706775).

Almost surely, 2^18617821 is an apocalyptic number.

It is an amenable number.

18617821 is a deficient number, since it is larger than the sum of its proper divisors (209279).

18617821 is an equidigital number, since it uses as much as digits as its factorization.

18617821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 209278.

The product of its digits is 5376, while the sum is 34.

The square root of 18617821 is about 4314.8373086363. The cubic root of 18617821 is about 265.0388978145.

The spelling of 18617821 in words is "eighteen million, six hundred seventeen thousand, eight hundred twenty-one".