218170721 has 2 divisors, whose sum is σ = 218170722. Its totient is φ = 218170720.

The previous prime is 218170699. The next prime is 218170739. The reversal of 218170721 is 127071812.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 118570321 + 99600400 = 10889^2 + 9980^2 .

It is a cyclic number.

It is not a de Polignac number, because 218170721 - 2⁶ = 218170657 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (218170621) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 109085360 + 109085361.

It is an arithmetic number, because the mean of its divisors is an integer number (109085361).

Almost surely, 2^218170721 is an apocalyptic number.

It is an amenable number.

218170721 is a deficient number, since it is larger than the sum of its proper divisors (1).

218170721 is an equidigital number, since it uses as much as digits as its factorization.

218170721 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1568, while the sum is 29.

The square root of 218170721 is about 14770.6032713630. The cubic root of 218170721 is about 602.0032311832.

The spelling of 218170721 in words is "two hundred eighteen million, one hundred seventy thousand, seven hundred twenty-one".