688403521 has 4 divisors (see below), whose sum is σ = 741357652. Its totient is φ = 635449392.

The previous prime is 688403473. The next prime is 688403533. The reversal of 688403521 is 125304886.

It is a happy number.

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

It can be written as a sum of positive squares in 2 ways, for example, as 148352400 + 540051121 = 12180^2 + 23239^2 .

It is a cyclic number.

It is not a de Polignac number, because 688403521 - 2¹¹ = 688401473 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (688403581) 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, 26477046 + ... + 26477071.

It is an arithmetic number, because the mean of its divisors is an integer number (185339413).

Almost surely, 2^688403521 is an apocalyptic number.

It is an amenable number.

688403521 is a deficient number, since it is larger than the sum of its proper divisors (52954131).

688403521 is a wasteful number, since it uses less digits than its factorization.

688403521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 52954130.

The product of its (nonzero) digits is 46080, while the sum is 37.

The square root of 688403521 is about 26237.4450166170. The cubic root of 688403521 is about 882.9735502005.

It can be divided in two parts, 68840 and 3521, that added together give a square (72361 = 269²).

The spelling of 688403521 in words is "six hundred eighty-eight million, four hundred three thousand, five hundred twenty-one".