18181257781 has 4 divisors (see below), whose sum is σ = 18187417612. Its totient is φ = 18175097952.

The previous prime is 18181257713. The next prime is 18181257803. The reversal of 18181257781 is 18775218181.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 11656657156 + 6524600625 = 107966^2 + 80775^2 .

It is a cyclic number.

It is not a de Polignac number, because 18181257781 - 2¹⁷ = 18181126709 is a prime.

It is a super-3 number, since 3×18181257781³ (a number of 32 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18181257181) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3075486 + ... + 3081391.

It is an arithmetic number, because the mean of its divisors is an integer number (4546854403).

Almost surely, 2^18181257781 is an apocalyptic number.

It is an amenable number.

18181257781 is a deficient number, since it is larger than the sum of its proper divisors (6159831).

18181257781 is an equidigital number, since it uses as much as digits as its factorization.

18181257781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6159830.

The product of its digits is 250880, while the sum is 49.

The spelling of 18181257781 in words is "eighteen billion, one hundred eighty-one million, two hundred fifty-seven thousand, seven hundred eighty-one".