216855921 has 4 divisors (see below), whose sum is σ = 289141232. Its totient is φ = 144570612.

The previous prime is 216855907. The next prime is 216855953. The reversal of 216855921 is 129558612.

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.

It is not a de Polignac number, because 216855921 - 2¹⁵ = 216823153 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 216855921.

It is not an unprimeable number, because it can be changed into a prime (216855971) 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, 36142651 + ... + 36142656.

It is an arithmetic number, because the mean of its divisors is an integer number (72285308).

Almost surely, 2^216855921 is an apocalyptic number.

It is an amenable number.

216855921 is a deficient number, since it is larger than the sum of its proper divisors (72285311).

216855921 is an equidigital number, since it uses as much as digits as its factorization.

216855921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 72285310.

The product of its digits is 43200, while the sum is 39.

The square root of 216855921 is about 14726.0286907231. The cubic root of 216855921 is about 600.7914749311.

The spelling of 216855921 in words is "two hundred sixteen million, eight hundred fifty-five thousand, nine hundred twenty-one".