687606821 has 6 divisors (see below), whose sum is σ = 755799366. Its totient is φ = 625097000.

The previous prime is 687606811. The next prime is 687606847. The reversal of 687606821 is 128606786.

It can be written as a sum of positive squares in only one way, i.e., 533101921 + 154504900 = 23089^2 + 12430^2 .

It is a de Polignac number, because none of the positive numbers 2^k-687606821 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (687606811) 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 5 ways as a sum of consecutive naturals, for example, 2841230 + ... + 2841471.

It is an arithmetic number, because the mean of its divisors is an integer number (125966561).

Almost surely, 2^687606821 is an apocalyptic number.

It is an amenable number.

687606821 is a deficient number, since it is larger than the sum of its proper divisors (68192545).

687606821 is a wasteful number, since it uses less digits than its factorization.

687606821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5682723 (or 5682712 counting only the distinct ones).

The product of its (nonzero) digits is 193536, while the sum is 44.

The square root of 687606821 is about 26222.2581216798. The cubic root of 687606821 is about 882.6327924145.

The spelling of 687606821 in words is "six hundred eighty-seven million, six hundred six thousand, eight hundred twenty-one".