18516521 has 4 divisors (see below), whose sum is σ = 18590544. Its totient is φ = 18442500.

The previous prime is 18516499. The next prime is 18516527. The reversal of 18516521 is 12561581.

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: 12561581 = 181 ⋅69401.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-18516521 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (18516527) 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, 36635 + ... + 37136.

It is an arithmetic number, because the mean of its divisors is an integer number (4647636).

Almost surely, 2^18516521 is an apocalyptic number.

It is an amenable number.

18516521 is a deficient number, since it is larger than the sum of its proper divisors (74023).

18516521 is an equidigital number, since it uses as much as digits as its factorization.

18516521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 74022.

The product of its digits is 2400, while the sum is 29.

The square root of 18516521 is about 4303.0827321817. The cubic root of 18516521 is about 264.5573290637.

The spelling of 18516521 in words is "eighteen million, five hundred sixteen thousand, five hundred twenty-one".