217385921 has 2 divisors, whose sum is σ = 217385922. Its totient is φ = 217385920.

The previous prime is 217385911. The next prime is 217385939. The reversal of 217385921 is 129583712.

217385921 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 201072400 + 16313521 = 14180^2 + 4039^2 .

It is a cyclic number.

It is not a de Polignac number, because 217385921 - 2²² = 213191617 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (217385911) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 108692960 + 108692961.

It is an arithmetic number, because the mean of its divisors is an integer number (108692961).

Almost surely, 2^217385921 is an apocalyptic number.

It is an amenable number.

217385921 is a deficient number, since it is larger than the sum of its proper divisors (1).

217385921 is an equidigital number, since it uses as much as digits as its factorization.

217385921 is an evil number, because the sum of its binary digits is even.

The product of its digits is 30240, while the sum is 38.

The square root of 217385921 is about 14744.0130561527. The cubic root of 217385921 is about 601.2805253324.

The spelling of 217385921 in words is "two hundred seventeen million, three hundred eighty-five thousand, nine hundred twenty-one".