18355681 has 4 divisors (see below), whose sum is σ = 18368532. Its totient is φ = 18342832.

The previous prime is 18355657. The next prime is 18355697. The reversal of 18355681 is 18655381.

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 640000 + 17715681 = 800^2 + 4209^2 .

It is a cyclic number.

It is not a de Polignac number, because 18355681 - 2⁷ = 18355553 is a prime.

It is a super-2 number, since 2×18355681² = 673862049947522, 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 18355681.

It is not an unprimeable number, because it can be changed into a prime (18355621) 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, 3970 + ... + 7243.

It is an arithmetic number, because the mean of its divisors is an integer number (4592133).

Almost surely, 2^18355681 is an apocalyptic number.

It is an amenable number.

18355681 is a deficient number, since it is larger than the sum of its proper divisors (12851).

18355681 is a wasteful number, since it uses less digits than its factorization.

18355681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12850.

The product of its digits is 28800, while the sum is 37.

The square root of 18355681 is about 4284.3530433427. The cubic root of 18355681 is about 263.7890925336.

The spelling of 18355681 in words is "eighteen million, three hundred fifty-five thousand, six hundred eighty-one".