686138921 has 24 divisors (see below), whose sum is σ = 818019720. Its totient is φ = 570087936.

The previous prime is 686138911. The next prime is 686138923. The reversal of 686138921 is 129831686.

It can be written as a sum of positive squares in 4 ways, for example, as 8265625 + 677873296 = 2875^2 + 26036^2 .

It is not a de Polignac number, because 686138921 - 2¹⁴ = 686122537 is a prime.

It is a super-2 number, since 2×686138921² = 941573237822088482, 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 (686138923) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 113975 + ... + 119843.

It is an arithmetic number, because the mean of its divisors is an integer number (34084155).

Almost surely, 2^686138921 is an apocalyptic number.

It is an amenable number.

686138921 is a deficient number, since it is larger than the sum of its proper divisors (131880799).

686138921 is a wasteful number, since it uses less digits than its factorization.

686138921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5945 (or 5922 counting only the distinct ones).

The product of its digits is 124416, while the sum is 44.

The square root of 686138921 is about 26194.2535873806. The cubic root of 686138921 is about 882.0042647490.

The spelling of 686138921 in words is "six hundred eighty-six million, one hundred thirty-eight thousand, nine hundred twenty-one".