720661 has 2 divisors, whose sum is σ = 720662. Its totient is φ = 720660.

The previous prime is 720653. The next prime is 720677. The reversal of 720661 is 166027.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 396900 + 323761 = 630^2 + 569^2 .

It is an emirp because it is prime and its reverse (166027) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 720661 - 2³ = 720653 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (720611) 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, 360330 + 360331.

It is an arithmetic number, because the mean of its divisors is an integer number (360331).

2⁷²⁰⁶⁶¹ is an apocalyptic number.

It is an amenable number.

720661 is a deficient number, since it is larger than the sum of its proper divisors (1).

720661 is an equidigital number, since it uses as much as digits as its factorization.

720661 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 504, while the sum is 22.

The square root of 720661 is about 848.9175460550. The cubic root of 720661 is about 89.6555143988.

Adding to 720661 its reverse (166027), we get a palindrome (886688).

The spelling of 720661 in words is "seven hundred twenty thousand, six hundred sixty-one".