685720921 has 4 divisors (see below), whose sum is σ = 709366500. Its totient is φ = 662075344.

The previous prime is 685720909. The next prime is 685720933. The reversal of 685720921 is 129027586.

It is a semiprime because it is the product of two primes.

It is an interprime number because it is at equal distance from previous prime (685720909) and next prime (685720933).

It can be written as a sum of positive squares in 2 ways, for example, as 535413321 + 150307600 = 23139^2 + 12260^2 .

It is a cyclic number.

It is not a de Polignac number, because 685720921 - 2⁷ = 685720793 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (685720421) 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, 11822746 + ... + 11822803.

It is an arithmetic number, because the mean of its divisors is an integer number (177341625).

Almost surely, 2^685720921 is an apocalyptic number.

It is an amenable number.

685720921 is a deficient number, since it is larger than the sum of its proper divisors (23645579).

685720921 is a wasteful number, since it uses less digits than its factorization.

685720921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 23645578.

The product of its (nonzero) digits is 60480, while the sum is 40.

The square root of 685720921 is about 26186.2735225919. The cubic root of 685720921 is about 881.8251209131.

The spelling of 685720921 in words is "six hundred eighty-five million, seven hundred twenty thousand, nine hundred twenty-one".