18643681 has 8 divisors (see below), whose sum is σ = 21359744. Its totient is φ = 15940800.

The previous prime is 18643657. The next prime is 18643697. The reversal of 18643681 is 18634681.

18643681 = T₄₉ + T₅₀ + ... + T₄₈₁.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 18643681 - 2⁵ = 18643649 is a prime.

It is a super-2 number, since 2×18643681² = 695173682459522, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 18643681.

It is not an unprimeable number, because it can be changed into a prime (18643081) 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 7 ways as a sum of consecutive naturals, for example, 45 + ... + 6106.

It is an arithmetic number, because the mean of its divisors is an integer number (2669968).

Almost surely, 2^18643681 is an apocalyptic number.

It is an amenable number.

18643681 is a deficient number, since it is larger than the sum of its proper divisors (2716063).

18643681 is an equidigital number, since it uses as much as digits as its factorization.

18643681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6591.

The product of its digits is 27648, while the sum is 37.

The square root of 18643681 is about 4317.8329055210. The cubic root of 18643681 is about 265.1615533248.

The spelling of 18643681 in words is "eighteen million, six hundred forty-three thousand, six hundred eighty-one".