21123031818 has 96 divisors (see below), whose sum is σ = 50713423488. Its totient is φ = 5844518400.

The previous prime is 21123031799. The next prime is 21123031819. The reversal of 21123031818 is 81813032112.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21123031819) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 1645003 + ... + 1657793.

It is an arithmetic number, because the mean of its divisors is an integer number (528264828).

Almost surely, 2^21123031818 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21123031818, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25356711744).

21123031818 is an abundant number, since it is smaller than the sum of its proper divisors (29590391670).

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

21123031818 is a wasteful number, since it uses less digits than its factorization.

21123031818 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12988 (or 12981 counting only the distinct ones).

The product of its (nonzero) digits is 2304, while the sum is 30.

The spelling of 21123031818 in words is "twenty-one billion, one hundred twenty-three million, thirty-one thousand, eight hundred eighteen".