685801021 has 2 divisors, whose sum is σ = 685801022. Its totient is φ = 685801020.

The previous prime is 685801007. The next prime is 685801037. The reversal of 685801021 is 120108586.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 682776900 + 3024121 = 26130^2 + 1739^2 .

It is a cyclic number.

It is not a de Polignac number, because 685801021 - 2¹¹ = 685798973 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (685801091) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 342900510 + 342900511.

It is an arithmetic number, because the mean of its divisors is an integer number (342900511).

Almost surely, 2^685801021 is an apocalyptic number.

It is an amenable number.

685801021 is a deficient number, since it is larger than the sum of its proper divisors (1).

685801021 is an equidigital number, since it uses as much as digits as its factorization.

685801021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3840, while the sum is 31.

The square root of 685801021 is about 26187.8029051694. The cubic root of 685801021 is about 881.8594553096.

The spelling of 685801021 in words is "six hundred eighty-five million, eight hundred one thousand, twenty-one".