686605921 has 2 divisors, whose sum is σ = 686605922. Its totient is φ = 686605920.

The previous prime is 686605903. The next prime is 686605957. The reversal of 686605921 is 129506686.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 652547025 + 34058896 = 25545^2 + 5836^2 .

It is a cyclic number.

It is not a de Polignac number, because 686605921 - 2⁵ = 686605889 is a prime.

It is not a weakly prime, because it can be changed into another prime (686605901) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 343302960 + 343302961.

It is an arithmetic number, because the mean of its divisors is an integer number (343302961).

Almost surely, 2^686605921 is an apocalyptic number.

It is an amenable number.

686605921 is a deficient number, since it is larger than the sum of its proper divisors (1).

686605921 is an equidigital number, since it uses as much as digits as its factorization.

686605921 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 155520, while the sum is 43.

The square root of 686605921 is about 26203.1662399795. The cubic root of 686605921 is about 882.2043226703.

The spelling of 686605921 in words is "six hundred eighty-six million, six hundred five thousand, nine hundred twenty-one".