18281993 has 4 divisors (see below), whose sum is σ = 18320640. Its totient is φ = 18243348.

The previous prime is 18281983. The next prime is 18282007. The reversal of 18281993 is 39918281.

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: 39918281 = 13 ⋅3070637.

It is a cyclic number.

It is not a de Polignac number, because 18281993 - 2⁶ = 18281929 is a prime.

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 18281993.

It is not an unprimeable number, because it can be changed into a prime (18281903) 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, 18605 + ... + 19562.

It is an arithmetic number, because the mean of its divisors is an integer number (4580160).

Almost surely, 2^18281993 is an apocalyptic number.

It is an amenable number.

18281993 is a deficient number, since it is larger than the sum of its proper divisors (38647).

18281993 is an equidigital number, since it uses as much as digits as its factorization.

18281993 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 38646.

The product of its digits is 31104, while the sum is 41.

The square root of 18281993 is about 4275.7447304534. The cubic root of 18281993 is about 263.4356295755.

The spelling of 18281993 in words is "eighteen million, two hundred eighty-one thousand, nine hundred ninety-three".