216221991 has 8 divisors (see below), whose sum is σ = 288563184. Its totient is φ = 144014400.

The previous prime is 216221983. The next prime is 216222001. The reversal of 216221991 is 199122612.

216221991 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 216221991 - 2³ = 216221983 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (216221921) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 29560 + ... + 36141.

It is an arithmetic number, because the mean of its divisors is an integer number (36070398).

Almost surely, 2^216221991 is an apocalyptic number.

216221991 is a deficient number, since it is larger than the sum of its proper divisors (72341193).

216221991 is a wasteful number, since it uses less digits than its factorization.

216221991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 66801.

The product of its digits is 3888, while the sum is 33.

The square root of 216221991 is about 14704.4888044434. The cubic root of 216221991 is about 600.2054768463.

The spelling of 216221991 in words is "two hundred sixteen million, two hundred twenty-one thousand, nine hundred ninety-one".