18991613 has 4 divisors (see below), whose sum is σ = 19002588. Its totient is φ = 18980640.

The previous prime is 18991589. The next prime is 18991627. The reversal of 18991613 is 31619981.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 6017209 + 12974404 = 2453^2 + 3602^2 .

It is a cyclic number.

It is not a de Polignac number, because 18991613 - 2¹⁶ = 18926077 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18991633) 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, 2258 + ... + 6563.

It is an arithmetic number, because the mean of its divisors is an integer number (4750647).

Almost surely, 2^18991613 is an apocalyptic number.

It is an amenable number.

18991613 is a deficient number, since it is larger than the sum of its proper divisors (10975).

18991613 is an equidigital number, since it uses as much as digits as its factorization.

18991613 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10974.

The product of its digits is 11664, while the sum is 38.

The square root of 18991613 is about 4357.9367824694. The cubic root of 18991613 is about 266.8008961381.

The spelling of 18991613 in words is "eighteen million, nine hundred ninety-one thousand, six hundred thirteen".