18278991 has 6 divisors (see below), whose sum is σ = 26403000. Its totient is φ = 12185988.

The previous prime is 18278987. The next prime is 18279013. The reversal of 18278991 is 19987281.

It is not a de Polignac number, because 18278991 - 2² = 18278987 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18278191) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1015491 + ... + 1015508.

It is an arithmetic number, because the mean of its divisors is an integer number (4400500).

Almost surely, 2^18278991 is an apocalyptic number.

18278991 is a deficient number, since it is larger than the sum of its proper divisors (8124009).

18278991 is a wasteful number, since it uses less digits than its factorization.

18278991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2031005 (or 2031002 counting only the distinct ones).

The product of its digits is 72576, while the sum is 45.

The square root of 18278991 is about 4275.3936660850. The cubic root of 18278991 is about 263.4212096114.

The spelling of 18278991 in words is "eighteen million, two hundred seventy-eight thousand, nine hundred ninety-one".