721663765 has 16 divisors (see below), whose sum is σ = 885678768. Its totient is φ = 564350976.

The previous prime is 721663717. The next prime is 721663777. The reversal of 721663765 is 567366127.

721663765 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It can be written as a sum of positive squares in 8 ways, for example, as 320302609 + 401361156 = 17897^2 + 20034^2 .

It is a cyclic number.

It is not a de Polignac number, because 721663765 - 2⁹ = 721663253 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 32497 + ... + 49993.

It is an arithmetic number, because the mean of its divisors is an integer number (55354923).

Almost surely, 2^721663765 is an apocalyptic number.

It is an amenable number.

721663765 is a deficient number, since it is larger than the sum of its proper divisors (164015003).

721663765 is a wasteful number, since it uses less digits than its factorization.

721663765 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17688.

The product of its digits is 317520, while the sum is 43.

The square root of 721663765 is about 26863.8002709967. The cubic root of 721663765 is about 896.9707890018.

The spelling of 721663765 in words is "seven hundred twenty-one million, six hundred sixty-three thousand, seven hundred sixty-five".