18687891978 has 96 divisors (see below), whose sum is σ = 48887879040. Its totient is φ = 5039936640.

The previous prime is 18687891967. The next prime is 18687891979. The reversal of 18687891978 is 87919878681.

It is not an unprimeable number, because it can be changed into a prime (18687891979) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 649048 + ... + 677228.

It is an arithmetic number, because the mean of its divisors is an integer number (509248740).

Almost surely, 2^18687891978 is an apocalyptic number.

18687891978 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 18687891978, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24443939520).

18687891978 is an abundant number, since it is smaller than the sum of its proper divisors (30199987062).

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

18687891978 is a wasteful number, since it uses less digits than its factorization.

18687891978 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 28492 (or 28489 counting only the distinct ones).

The product of its digits is 97542144, while the sum is 72.

The spelling of 18687891978 in words is "eighteen billion, six hundred eighty-seven million, eight hundred ninety-one thousand, nine hundred seventy-eight".