635991 has 4 divisors (see below), whose sum is σ = 847992. Its totient is φ = 423992.

The previous prime is 635989. The next prime is 636017. The reversal of 635991 is 199536.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 635991 - 2¹ = 635989 is a prime.

It is a D-number.

It is a plaindrome in base 14.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (635981) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 105996 + ... + 106001.

It is an arithmetic number, because the mean of its divisors is an integer number (211998).

2⁶³⁵⁹⁹¹ is an apocalyptic number.

635991 is a deficient number, since it is larger than the sum of its proper divisors (212001).

635991 is a wasteful number, since it uses less digits than its factorization.

635991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 212000.

The product of its digits is 7290, while the sum is 33.

The square root of 635991 is about 797.4904388142. The cubic root of 635991 is about 85.9970703888.

The spelling of 635991 in words is "six hundred thirty-five thousand, nine hundred ninety-one".