688691405 has 4 divisors (see below), whose sum is σ = 826429692. Its totient is φ = 550953120.

The previous prime is 688691387. The next prime is 688691407. The reversal of 688691405 is 504196886.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 504196886 = 2 ⋅252098443.

It can be written as a sum of positive squares in 2 ways, for example, as 253510084 + 435181321 = 15922^2 + 20861^2 .

It is not a de Polignac number, because 688691405 - 2⁸ = 688691149 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 688691405.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (688691407) 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 in 3 ways as a sum of consecutive naturals, for example, 68869136 + ... + 68869145.

It is an arithmetic number, because the mean of its divisors is an integer number (206607423).

Almost surely, 2^688691405 is an apocalyptic number.

It is an amenable number.

688691405 is a deficient number, since it is larger than the sum of its proper divisors (137738287).

688691405 is a wasteful number, since it uses less digits than its factorization.

688691405 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 137738286.

The product of its (nonzero) digits is 414720, while the sum is 47.

The square root of 688691405 is about 26242.9305718702. The cubic root of 688691405 is about 883.0966168439.

The spelling of 688691405 in words is "six hundred eighty-eight million, six hundred ninety-one thousand, four hundred five".