720997661 has 4 divisors (see below), whose sum is σ = 721110012. Its totient is φ = 720885312.

The previous prime is 720997649. The next prime is 720997679. The reversal of 720997661 is 166799027.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 166799027 = 139 ⋅1199993.

It can be written as a sum of positive squares in 2 ways, for example, as 246019225 + 474978436 = 15685^2 + 21794^2 .

It is a cyclic number.

It is not a de Polignac number, because 720997661 - 2²² = 716803357 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (720990661) 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 in 3 ways as a sum of consecutive naturals, for example, 45926 + ... + 59591.

It is an arithmetic number, because the mean of its divisors is an integer number (180277503).

Almost surely, 2^720997661 is an apocalyptic number.

It is an amenable number.

720997661 is a deficient number, since it is larger than the sum of its proper divisors (112351).

720997661 is a wasteful number, since it uses less digits than its factorization.

720997661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 112350.

The product of its (nonzero) digits is 285768, while the sum is 47.

The square root of 720997661 is about 26851.3996097038. The cubic root of 720997661 is about 896.6947325798.

The spelling of 720997661 in words is "seven hundred twenty million, nine hundred ninety-seven thousand, six hundred sixty-one".