18040781 has 4 divisors (see below), whose sum is σ = 19680864. Its totient is φ = 16400700.

The previous prime is 18040777. The next prime is 18040817. The reversal of 18040781 is 18704081.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 18704081 = 11 ⋅1700371.

It is a cyclic number.

It is not a de Polignac number, because 18040781 - 2² = 18040777 is a prime.

It is a super-2 number, since 2×18040781² = 650939558179922, which contains 22 as substring.

It is a Duffinian number.

It is a plaindrome in base 16.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18040751) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 820025 + ... + 820046.

It is an arithmetic number, because the mean of its divisors is an integer number (4920216).

Almost surely, 2^18040781 is an apocalyptic number.

18040781 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

18040781 is a deficient number, since it is larger than the sum of its proper divisors (1640083).

18040781 is a wasteful number, since it uses less digits than its factorization.

18040781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1640082.

The product of its (nonzero) digits is 1792, while the sum is 29.

The square root of 18040781 is about 4247.4440549582. Note that the first 3 decimals coincide. The cubic root of 18040781 is about 262.2719095000.

The spelling of 18040781 in words is "eighteen million, forty thousand, seven hundred eighty-one".