216972991 has 4 divisors (see below), whose sum is σ = 217242000. Its totient is φ = 216703984.

The previous prime is 216972971. The next prime is 216972997. The reversal of 216972991 is 199279612.

It is a happy number.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-216972991 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 (216972997) 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, 133291 + ... + 134908.

It is an arithmetic number, because the mean of its divisors is an integer number (54310500).

Almost surely, 2^216972991 is an apocalyptic number.

216972991 is a deficient number, since it is larger than the sum of its proper divisors (269009).

216972991 is an equidigital number, since it uses as much as digits as its factorization.

216972991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 269008.

The product of its digits is 122472, while the sum is 46.

The square root of 216972991 is about 14730.0030889338. The cubic root of 216972991 is about 600.8995682136.

The spelling of 216972991 in words is "two hundred sixteen million, nine hundred seventy-two thousand, nine hundred ninety-one".