721644361 has 6 divisors (see below), whose sum is σ = 738818970. Its totient is φ = 704860128.

The previous prime is 721644317. The next prime is 721644367. The reversal of 721644361 is 163446127.

It can be written as a sum of positive squares in only one way, i.e., 447576336 + 274068025 = 21156^2 + 16555^2 .

It is not a de Polignac number, because 721644361 - 2⁷ = 721644233 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (721644367) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 193296 + ... + 196993.

It is an arithmetic number, because the mean of its divisors is an integer number (123136495).

Almost surely, 2^721644361 is an apocalyptic number.

It is an amenable number.

721644361 is a deficient number, since it is larger than the sum of its proper divisors (17174609).

721644361 is an equidigital number, since it uses as much as digits as its factorization.

721644361 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 390375 (or 390332 counting only the distinct ones).

The product of its digits is 24192, while the sum is 34.

The square root of 721644361 is about 26863.4391134121. The cubic root of 721644361 is about 896.9627497190.

The spelling of 721644361 in words is "seven hundred twenty-one million, six hundred forty-four thousand, three hundred sixty-one".