18439478921 has 2 divisors, whose sum is σ = 18439478922. Its totient is φ = 18439478920.

The previous prime is 18439478917. The next prime is 18439478983. The reversal of 18439478921 is 12987493481.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18269306896 + 170172025 = 135164^2 + 13045^2 .

It is an emirp because it is prime and its reverse (12987493481) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 18439478921 - 2² = 18439478917 is a prime.

It is not a weakly prime, because it can be changed into another prime (18439478021) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9219739460 + 9219739461.

It is an arithmetic number, because the mean of its divisors is an integer number (9219739461).

Almost surely, 2^18439478921 is an apocalyptic number.

It is an amenable number.

18439478921 is a deficient number, since it is larger than the sum of its proper divisors (1).

18439478921 is an equidigital number, since it uses as much as digits as its factorization.

18439478921 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3483648, while the sum is 56.

The spelling of 18439478921 in words is "eighteen billion, four hundred thirty-nine million, four hundred seventy-eight thousand, nine hundred twenty-one".