18668981 has 4 divisors (see below), whose sum is σ = 19124364. Its totient is φ = 18213600.

The previous prime is 18668959. The next prime is 18669017. The reversal of 18668981 is 18986681.

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 6002500 + 12666481 = 2450^2 + 3559^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-18668981 is a prime.

It is a super-2 number, since 2×18668981² = 697061703156722, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18668921) 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, 227630 + ... + 227711.

It is an arithmetic number, because the mean of its divisors is an integer number (4781091).

Almost surely, 2^18668981 is an apocalyptic number.

It is an amenable number.

18668981 is a deficient number, since it is larger than the sum of its proper divisors (455383).

18668981 is an equidigital number, since it uses as much as digits as its factorization.

18668981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 455382.

The product of its digits is 165888, while the sum is 47.

The square root of 18668981 is about 4320.7616226772. The cubic root of 18668981 is about 265.2814430076.

The spelling of 18668981 in words is "eighteen million, six hundred sixty-eight thousand, nine hundred eighty-one".