18416821 has 4 divisors (see below), whose sum is σ = 19010944. Its totient is φ = 17822700.

The previous prime is 18416819. The next prime is 18416837. The reversal of 18416821 is 12861481.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 18416821 - 2¹ = 18416819 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (31), and also a Moran number because the ratio is a prime number: 594091 = 18416821 / (1 + 8 + 4 + 1 + 6 + 8 + 2 + 1).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18416851) 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, 297015 + ... + 297076.

It is an arithmetic number, because the mean of its divisors is an integer number (4752736).

Almost surely, 2^18416821 is an apocalyptic number.

It is an amenable number.

18416821 is a deficient number, since it is larger than the sum of its proper divisors (594123).

18416821 is an equidigital number, since it uses as much as digits as its factorization.

18416821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 594122.

The product of its digits is 3072, while the sum is 31.

The square root of 18416821 is about 4291.4823779202. The cubic root of 18416821 is about 264.0816484906.

The spelling of 18416821 in words is "eighteen million, four hundred sixteen thousand, eight hundred twenty-one".