217920813 has 16 divisors (see below), whose sum is σ = 317316096. Its totient is φ = 131931440.

The previous prime is 217920779. The next prime is 217920817. The reversal of 217920813 is 318029712.

It is a cyclic number.

It is not a de Polignac number, because 217920813 - 2⁹ = 217920301 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (33).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (217920817) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 33406 + ... + 39392.

It is an arithmetic number, because the mean of its divisors is an integer number (19832256).

Almost surely, 2^217920813 is an apocalyptic number.

It is an amenable number.

217920813 is a deficient number, since it is larger than the sum of its proper divisors (99395283).

217920813 is a wasteful number, since it uses less digits than its factorization.

217920813 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7104.

The product of its (nonzero) digits is 6048, while the sum is 33.

The square root of 217920813 is about 14762.1412064781. The cubic root of 217920813 is about 601.7732844959.

The spelling of 217920813 in words is "two hundred seventeen million, nine hundred twenty thousand, eight hundred thirteen".