217105921 has 2 divisors, whose sum is σ = 217105922. Its totient is φ = 217105920.

The previous prime is 217105909. The next prime is 217105949. The reversal of 217105921 is 129501712.

It is an a-pointer prime, because the next prime (217105949) can be obtained adding 217105921 to its sum of digits (28).

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 166126321 + 50979600 = 12889^2 + 7140^2 .

It is a cyclic number.

It is not a de Polignac number, because 217105921 - 2¹³ = 217097729 is a prime.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 217105921.

It is not a weakly prime, because it can be changed into another prime (217105991) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 108552960 + 108552961.

It is an arithmetic number, because the mean of its divisors is an integer number (108552961).

Almost surely, 2^217105921 is an apocalyptic number.

It is an amenable number.

217105921 is a deficient number, since it is larger than the sum of its proper divisors (1).

217105921 is an equidigital number, since it uses as much as digits as its factorization.

217105921 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1260, while the sum is 28.

The square root of 217105921 is about 14734.5146170480. The cubic root of 217105921 is about 601.0222582502.

The spelling of 217105921 in words is "two hundred seventeen million, one hundred five thousand, nine hundred twenty-one".