216218991 has 4 divisors (see below), whose sum is σ = 288291992. Its totient is φ = 144145992.

The previous prime is 216218963. The next prime is 216219001. The reversal of 216218991 is 199812612.

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

It is not a de Polignac number, because 216218991 - 2¹⁷ = 216087919 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 (216218911) 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, 36036496 + ... + 36036501.

It is an arithmetic number, because the mean of its divisors is an integer number (72072998).

Almost surely, 2^216218991 is an apocalyptic number.

216218991 is a deficient number, since it is larger than the sum of its proper divisors (72073001).

216218991 is an equidigital number, since it uses as much as digits as its factorization.

216218991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 72073000.

The product of its digits is 15552, while the sum is 39.

The square root of 216218991 is about 14704.3867944229. The cubic root of 216218991 is about 600.2027009573.

The spelling of 216218991 in words is "two hundred sixteen million, two hundred eighteen thousand, nine hundred ninety-one".