18993181 has 2 divisors, whose sum is σ = 18993182. Its totient is φ = 18993180.

The previous prime is 18993119. The next prime is 18993203. The reversal of 18993181 is 18139981.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16240900 + 2752281 = 4030^2 + 1659^2 .

It is an emirp because it is prime and its reverse (18139981) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 18993181 - 2⁷ = 18993053 is a prime.

It is a super-2 number, since 2×18993181² = 721481848997522, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18993881) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9496590 + 9496591.

It is an arithmetic number, because the mean of its divisors is an integer number (9496591).

Almost surely, 2^18993181 is an apocalyptic number.

It is an amenable number.

18993181 is a deficient number, since it is larger than the sum of its proper divisors (1).

18993181 is an equidigital number, since it uses as much as digits as its factorization.

18993181 is an evil number, because the sum of its binary digits is even.

The product of its digits is 15552, while the sum is 40.

The square root of 18993181 is about 4358.1166804022. The cubic root of 18993181 is about 266.8082385422.

The spelling of 18993181 in words is "eighteen million, nine hundred ninety-three thousand, one hundred eighty-one".