635821 has 2 divisors, whose sum is σ = 635822. Its totient is φ = 635820.

The previous prime is 635813. The next prime is 635837. The reversal of 635821 is 128536.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 509796 + 126025 = 714^2 + 355^2 .

It is a cyclic number.

It is not a de Polignac number, because 635821 - 2³ = 635813 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (635801) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 317910 + 317911.

It is an arithmetic number, because the mean of its divisors is an integer number (317911).

2⁶³⁵⁸²¹ is an apocalyptic number.

It is an amenable number.

635821 is a deficient number, since it is larger than the sum of its proper divisors (1).

635821 is an equidigital number, since it uses as much as digits as its factorization.

635821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1440, while the sum is 25.

The square root of 635821 is about 797.3838473408. The cubic root of 635821 is about 85.9894073847.

The spelling of 635821 in words is "six hundred thirty-five thousand, eight hundred twenty-one".