216664891 has 4 divisors (see below), whose sum is σ = 216749392. Its totient is φ = 216580392.

The previous prime is 216664879. The next prime is 216664909. The reversal of 216664891 is 198466612.

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 216664891 - 2²¹ = 214567739 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (216664841) 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, 38280 + ... + 43573.

It is an arithmetic number, because the mean of its divisors is an integer number (54187348).

Almost surely, 2^216664891 is an apocalyptic number.

216664891 is a deficient number, since it is larger than the sum of its proper divisors (84501).

216664891 is an equidigital number, since it uses as much as digits as its factorization.

216664891 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 84500.

The product of its digits is 124416, while the sum is 43.

The square root of 216664891 is about 14719.5411273586. The cubic root of 216664891 is about 600.6150092056.

The spelling of 216664891 in words is "two hundred sixteen million, six hundred sixty-four thousand, eight hundred ninety-one".