664173721 has 2 divisors, whose sum is σ = 664173722. Its totient is φ = 664173720.

The previous prime is 664173707. The next prime is 664173749. The reversal of 664173721 is 127371466.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 441000000 + 223173721 = 21000^2 + 14939^2 .

It is a cyclic number.

It is not a de Polignac number, because 664173721 - 2²⁵ = 630619289 is a prime.

It is a super-2 number, since 2×664173721² = 882253463333971682, which contains 22 as substring.

It is equal to p_34491826 and since 664173721 and 34491826 have the same sum of digits, it is a Honaker prime.

It is not a weakly prime, because it can be changed into another prime (664173761) 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 as a sum of consecutive naturals, namely, 332086860 + 332086861.

It is an arithmetic number, because the mean of its divisors is an integer number (332086861).

Almost surely, 2^664173721 is an apocalyptic number.

It is an amenable number.

664173721 is a deficient number, since it is larger than the sum of its proper divisors (1).

664173721 is an equidigital number, since it uses as much as digits as its factorization.

664173721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 42336, while the sum is 37.

The square root of 664173721 is about 25771.5680741394. The cubic root of 664173721 is about 872.4902103154.

The spelling of 664173721 in words is "six hundred sixty-four million, one hundred seventy-three thousand, seven hundred twenty-one".