642721816818 has 64 divisors (see below), whose sum is σ = 1468968359040. Its totient is φ = 208152504000.

The previous prime is 642721816813. The next prime is 642721816819. The reversal of 642721816818 is 818618127246.

It is a Harshad number since it is a multiple of its sum of digits (54).

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (642721816813) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 1171153 + ... + 1630043.

It is an arithmetic number, because the mean of its divisors is an integer number (22952630610).

Almost surely, 2^642721816818 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 642721816818, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (734484179520).

642721816818 is an abundant number, since it is smaller than the sum of its proper divisors (826246542222).

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

642721816818 is a wasteful number, since it uses less digits than its factorization.

642721816818 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 459640 (or 459634 counting only the distinct ones).

The product of its digits is 2064384, while the sum is 54.

The spelling of 642721816818 in words is "six hundred forty-two billion, seven hundred twenty-one million, eight hundred sixteen thousand, eight hundred eighteen".