18478991 has 4 divisors (see below), whose sum is σ = 18620184. Its totient is φ = 18337800.

The previous prime is 18478973. The next prime is 18479009. The reversal of 18478991 is 19987481.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 19987481 = 719 ⋅27799.

It is an interprime number because it is at equal distance from previous prime (18478973) and next prime (18479009).

It is a cyclic number.

It is not a de Polignac number, because 18478991 - 2¹⁰ = 18477967 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 (18478931) 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, 70400 + ... + 70661.

It is an arithmetic number, because the mean of its divisors is an integer number (4655046).

Almost surely, 2^18478991 is an apocalyptic number.

18478991 is a deficient number, since it is larger than the sum of its proper divisors (141193).

18478991 is a wasteful number, since it uses less digits than its factorization.

18478991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 141192.

The product of its digits is 145152, while the sum is 47.

The square root of 18478991 is about 4298.7196931179. The cubic root of 18478991 is about 264.3784698317.

The spelling of 18478991 in words is "eighteen million, four hundred seventy-eight thousand, nine hundred ninety-one".