18991563 has 4 divisors (see below), whose sum is σ = 25322088. Its totient is φ = 12661040.

The previous prime is 18991559. The next prime is 18991573. The reversal of 18991563 is 36519981.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 36519981 = 3 ⋅12173327.

It is a cyclic number.

It is not a de Polignac number, because 18991563 - 2² = 18991559 is a prime.

It is not an unprimeable number, because it can be changed into a prime (18991573) 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, 3165258 + ... + 3165263.

It is an arithmetic number, because the mean of its divisors is an integer number (6330522).

Almost surely, 2^18991563 is an apocalyptic number.

18991563 is a deficient number, since it is larger than the sum of its proper divisors (6330525).

18991563 is an equidigital number, since it uses as much as digits as its factorization.

18991563 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6330524.

The product of its digits is 58320, while the sum is 42.

The square root of 18991563 is about 4357.9310458060. The cubic root of 18991563 is about 266.8006619987.

The spelling of 18991563 in words is "eighteen million, nine hundred ninety-one thousand, five hundred sixty-three".