18138781 has 4 divisors (see below), whose sum is σ = 18169564. Its totient is φ = 18108000.

The previous prime is 18138767. The next prime is 18138797. The reversal of 18138781 is 18783181.

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 12013156 + 6125625 = 3466^2 + 2475^2 .

It is a cyclic number.

It is not a de Polignac number, because 18138781 - 2¹¹ = 18136733 is a prime.

It is a super-2 number, since 2×18138781² = 658030752331922, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 18138781.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18138721) 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, 14490 + ... + 15691.

It is an arithmetic number, because the mean of its divisors is an integer number (4542391).

Almost surely, 2^18138781 is an apocalyptic number.

It is an amenable number.

18138781 is a deficient number, since it is larger than the sum of its proper divisors (30783).

18138781 is an equidigital number, since it uses as much as digits as its factorization.

18138781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 30782.

The product of its digits is 10752, while the sum is 37.

The square root of 18138781 is about 4258.9647803193. The cubic root of 18138781 is about 262.7459511906.

The spelling of 18138781 in words is "eighteen million, one hundred thirty-eight thousand, seven hundred eighty-one".