18991278 has 48 divisors (see below), whose sum is σ = 44428176. Its totient is φ = 5840640.

The previous prime is 18991267. The next prime is 18991283. The reversal of 18991278 is 87219981.

It is a congruent number.

It is an unprimeable number.

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 23 ways as a sum of consecutive naturals, for example, 15633 + ... + 16803.

It is an arithmetic number, because the mean of its divisors is an integer number (925587).

Almost surely, 2^18991278 is an apocalyptic number.

18991278 is a gapful number since it is divisible by the number (18) formed by its first and last digit.

It is a practical number, because each smaller number is the sum of distinct divisors of 18991278, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (22214088).

18991278 is an abundant number, since it is smaller than the sum of its proper divisors (25436898).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

18991278 is a wasteful number, since it uses less digits than its factorization.

18991278 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1249 (or 1246 counting only the distinct ones).

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

The square root of 18991278 is about 4357.8983466804. The cubic root of 18991278 is about 266.7993273961.

The spelling of 18991278 in words is "eighteen million, nine hundred ninety-one thousand, two hundred seventy-eight".