18539681 has 4 divisors (see below), whose sum is σ = 18673200. Its totient is φ = 18406164.

The previous prime is 18539663. The next prime is 18539683. The reversal of 18539681 is 18693581.

18539681 = 294² + 295² + ... + 432².

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: 18693581 = 41 ⋅455941.

It is a cyclic number.

It is not a de Polignac number, because 18539681 - 2⁶ = 18539617 is a prime.

It is a super-4 number, since 4×18539681⁴ (a number of 30 digits) contains 4444 as substring. Note that it is a super-d number also for d = 2.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (18539683) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 66551 + ... + 66828.

It is an arithmetic number, because the mean of its divisors is an integer number (4668300).

Almost surely, 2^18539681 is an apocalyptic number.

It is an amenable number.

18539681 is a deficient number, since it is larger than the sum of its proper divisors (133519).

18539681 is a wasteful number, since it uses less digits than its factorization.

18539681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 133518.

The product of its digits is 51840, while the sum is 41.

The square root of 18539681 is about 4305.7729851909. The cubic root of 18539681 is about 264.6675836656.

The spelling of 18539681 in words is "eighteen million, five hundred thirty-nine thousand, six hundred eighty-one".