687786821 has 4 divisors (see below), whose sum is σ = 706375692. Its totient is φ = 669197952.

The previous prime is 687786809. The next prime is 687786829. The reversal of 687786821 is 128687786.

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 571449025 + 116337796 = 23905^2 + 10786^2 .

It is a cyclic number.

It is not a de Polignac number, because 687786821 - 2¹⁴ = 687770437 is a prime.

It is a super-2 number, since 2×687786821² = 946101422282572082, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (687786829) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 9294380 + ... + 9294453.

It is an arithmetic number, because the mean of its divisors is an integer number (176593923).

Almost surely, 2^687786821 is an apocalyptic number.

It is an amenable number.

687786821 is a deficient number, since it is larger than the sum of its proper divisors (18588871).

687786821 is a wasteful number, since it uses less digits than its factorization.

687786821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18588870.

The product of its digits is 1806336, while the sum is 53.

The square root of 687786821 is about 26225.6900957820. The cubic root of 687786821 is about 882.7098034992.

The spelling of 687786821 in words is "six hundred eighty-seven million, seven hundred eighty-six thousand, eight hundred twenty-one".