720731681 has 2 divisors, whose sum is σ = 720731682. Its totient is φ = 720731680.

The previous prime is 720731639. The next prime is 720731689. The reversal of 720731681 is 186137027.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 711022225 + 9709456 = 26665^2 + 3116^2 .

It is an emirp because it is prime and its reverse (186137027) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-720731681 is a prime.

It is a super-2 number, since 2×720731681² = 1038908311994171522, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (720731689) 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, 360365840 + 360365841.

It is an arithmetic number, because the mean of its divisors is an integer number (360365841).

Almost surely, 2^720731681 is an apocalyptic number.

It is an amenable number.

720731681 is a deficient number, since it is larger than the sum of its proper divisors (1).

720731681 is an equidigital number, since it uses as much as digits as its factorization.

720731681 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 14112, while the sum is 35.

The square root of 720731681 is about 26846.4463383890. The cubic root of 720731681 is about 896.5844538128.

The spelling of 720731681 in words is "seven hundred twenty million, seven hundred thirty-one thousand, six hundred eighty-one".