18813981 has 4 divisors (see below), whose sum is σ = 25085312.
Its totient is φ = 12542652.
The previous prime is 18813961. The next prime is 18813983. The reversal of 18813981 is 18931881.
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: 18931881 = 3 ⋅6310627.
It is not a de Polignac number, because 18813981 - 29 = 18813469 is a prime.
It is a super-2 number, since 2×188139812 = 707931762136722, 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 (18813983) 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, 3135661 + ... + 3135666.
It is an arithmetic number, because the mean of its divisors is an integer number (6271328).
Almost surely, 218813981 is an apocalyptic number.
It is an amenable number.
18813981 is a deficient number, since it is larger than the sum of its proper divisors (6271331).
18813981 is an equidigital number, since it uses as much as digits as its factorization.
18813981 is an evil number, because the sum of its binary digits is even.
The sum of its prime factors is 6271330.
The product of its digits is 13824, while the sum is 39.
The square root of 18813981 is about 4337.5086167061.
The cubic root of 18813981 is about 265.9664768276.
The spelling of 18813981 in words is "eighteen million, eight hundred thirteen thousand, nine hundred eighty-one".