18921538 has 4 divisors (see below), whose sum is σ = 28382310. Its totient is φ = 9460768.

The previous prime is 18921533. The next prime is 18921547. The reversal of 18921538 is 83512981.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 83512981 = 337 ⋅247813.

It can be written as a sum of positive squares in only one way, i.e., 18378369 + 543169 = 4287^2 + 737^2 .

It is a junction number, because it is equal to n+sod(n) for n = 18921497 and 18921506.

It is not an unprimeable number, because it can be changed into a prime (18921533) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 4730383 + ... + 4730386.

Almost surely, 2^18921538 is an apocalyptic number.

18921538 is a deficient number, since it is larger than the sum of its proper divisors (9460772).

18921538 is an equidigital number, since it uses as much as digits as its factorization.

18921538 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9460771.

The product of its digits is 17280, while the sum is 37.

The square root of 18921538 is about 4349.8894238819. The cubic root of 18921538 is about 266.4723455846.

The spelling of 18921538 in words is "eighteen million, nine hundred twenty-one thousand, five hundred thirty-eight".