720809 has 4 divisors (see below), whose sum is σ = 737616. Its totient is φ = 704004.

The previous prime is 720793. The next prime is 720829. The reversal of 720809 is 908027.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 908027 = 41 ⋅22147.

It is a cyclic number.

It is not a de Polignac number, because 720809 - 2⁴ = 720793 is a prime.

It is a super-2 number, since 2×720809² = 1039131228962, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (720829) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8339 + ... + 8424.

It is an arithmetic number, because the mean of its divisors is an integer number (184404).

2⁷²⁰⁸⁰⁹ is an apocalyptic number.

It is an amenable number.

720809 is a deficient number, since it is larger than the sum of its proper divisors (16807).

720809 is a wasteful number, since it uses less digits than its factorization.

720809 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16806.

The product of its (nonzero) digits is 1008, while the sum is 26.

The square root of 720809 is about 849.0047114121. The cubic root of 720809 is about 89.6616514072.

The spelling of 720809 in words is "seven hundred twenty thousand, eight hundred nine".