217189981 has 8 divisors (see below), whose sum is σ = 218345400. Its totient is φ = 216038400.

The previous prime is 217189979. The next prime is 217190003. The reversal of 217189981 is 189981712.

It can be written as a sum of positive squares in 4 ways, for example, as 3006756 + 214183225 = 1734^2 + 14635^2 .

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

It is a cyclic number.

It is not a de Polignac number, because 217189981 - 2¹ = 217189979 is a prime.

It is a super-2 number, since 2×217189981² = 94342975693560722, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (217189081) 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, 233325 + ... + 234253.

It is an arithmetic number, because the mean of its divisors is an integer number (27293175).

Almost surely, 2^217189981 is an apocalyptic number.

It is an amenable number.

217189981 is a deficient number, since it is larger than the sum of its proper divisors (1155419).

217189981 is an equidigital number, since it uses as much as digits as its factorization.

217189981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1919.

The product of its digits is 72576, while the sum is 46.

The square root of 217189981 is about 14737.3668272185. The cubic root of 217189981 is about 601.0998170316.

The spelling of 217189981 in words is "two hundred seventeen million, one hundred eighty-nine thousand, nine hundred eighty-one".