217209989 has 2 divisors, whose sum is σ = 217209990. Its totient is φ = 217209988.

The previous prime is 217209917. The next prime is 217209991. The reversal of 217209989 is 989902712.

It is a happy number.

217209989 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 118048225 + 99161764 = 10865^2 + 9958^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-217209989 is a prime.

Together with 217209991, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (217209089) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 108604994 + 108604995.

It is an arithmetic number, because the mean of its divisors is an integer number (108604995).

Almost surely, 2^217209989 is an apocalyptic number.

It is an amenable number.

217209989 is a deficient number, since it is larger than the sum of its proper divisors (1).

217209989 is an equidigital number, since it uses as much as digits as its factorization.

217209989 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 163296, while the sum is 47.

The square root of 217209989 is about 14738.0456302727. The cubic root of 217209989 is about 601.1182746600.

The spelling of 217209989 in words is "two hundred seventeen million, two hundred nine thousand, nine hundred eighty-nine".