18216815 has 4 divisors (see below), whose sum is σ = 21860184. Its totient is φ = 14573448.

The previous prime is 18216811. The next prime is 18216817. The reversal of 18216815 is 51861281.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 18216815 - 2² = 18216811 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18216811) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1821677 + ... + 1821686.

It is an arithmetic number, because the mean of its divisors is an integer number (5465046).

Almost surely, 2^18216815 is an apocalyptic number.

18216815 is a deficient number, since it is larger than the sum of its proper divisors (3643369).

18216815 is an equidigital number, since it uses as much as digits as its factorization.

18216815 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3643368.

The product of its digits is 3840, while the sum is 32.

The square root of 18216815 is about 4268.1160949534. The cubic root of 18216815 is about 263.1221945150.

The spelling of 18216815 in words is "eighteen million, two hundred sixteen thousand, eight hundred fifteen".