18438421 has 4 divisors (see below), whose sum is σ = 19523052. Its totient is φ = 17353792.

The previous prime is 18438391. The next prime is 18438437. The reversal of 18438421 is 12483481.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12483481 = 839 ⋅14879.

It can be written as a sum of positive squares in 2 ways, for example, as 11088900 + 7349521 = 3330^2 + 2711^2 .

It is a cyclic number.

It is not a de Polignac number, because 18438421 - 2¹³ = 18430229 is a prime.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18438481) 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, 542290 + ... + 542323.

It is an arithmetic number, because the mean of its divisors is an integer number (4880763).

Almost surely, 2^18438421 is an apocalyptic number.

It is an amenable number.

18438421 is a deficient number, since it is larger than the sum of its proper divisors (1084631).

18438421 is a wasteful number, since it uses less digits than its factorization.

18438421 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1084630.

The product of its digits is 6144, while the sum is 31.

The square root of 18438421 is about 4293.9982533764. The cubic root of 18438421 is about 264.1848500698.

The spelling of 18438421 in words is "eighteen million, four hundred thirty-eight thousand, four hundred twenty-one".