721739561 has 2 divisors, whose sum is σ = 721739562. Its totient is φ = 721739560.

The previous prime is 721739533. The next prime is 721739593. The reversal of 721739561 is 165937127.

721739561 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 465739561 + 256000000 = 21581^2 + 16000^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-721739561 is a prime.

It is a super-3 number, since 3×721739561³ (a number of 28 digits) contains 333 as substring.

It is not a weakly prime, because it can be changed into another prime (721739521) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 360869780 + 360869781.

It is an arithmetic number, because the mean of its divisors is an integer number (360869781).

Almost surely, 2^721739561 is an apocalyptic number.

It is an amenable number.

721739561 is a deficient number, since it is larger than the sum of its proper divisors (1).

721739561 is an equidigital number, since it uses as much as digits as its factorization.

721739561 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 79380, while the sum is 41.

The square root of 721739561 is about 26865.2109800016. The cubic root of 721739561 is about 897.0021907067.

The spelling of 721739561 in words is "seven hundred twenty-one million, seven hundred thirty-nine thousand, five hundred sixty-one".