721647761 has 2 divisors, whose sum is σ = 721647762. Its totient is φ = 721647760.

The previous prime is 721647743. The next prime is 721647779. The reversal of 721647761 is 167746127.

It is a balanced prime because it is at equal distance from previous prime (721647743) and next prime (721647779).

It can be written as a sum of positive squares in only one way, i.e., 668998225 + 52649536 = 25865^2 + 7256^2 .

It is a cyclic number.

It is not a de Polignac number, because 721647761 - 2¹⁴ = 721631377 is a prime.

It is not a weakly prime, because it can be changed into another prime (721647361) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 360823880 + 360823881.

It is an arithmetic number, because the mean of its divisors is an integer number (360823881).

Almost surely, 2^721647761 is an apocalyptic number.

It is an amenable number.

721647761 is a deficient number, since it is larger than the sum of its proper divisors (1).

721647761 is an equidigital number, since it uses as much as digits as its factorization.

721647761 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 98784, while the sum is 41.

The square root of 721647761 is about 26863.5023963742. The cubic root of 721647761 is about 896.9641583855.

The spelling of 721647761 in words is "seven hundred twenty-one million, six hundred forty-seven thousand, seven hundred sixty-one".