637991 has 8 divisors (see below), whose sum is σ = 672144. Its totient is φ = 604800.

The previous prime is 637939. The next prime is 638023. The reversal of 637991 is 199736.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 637991 - 2¹⁰ = 636967 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (637291) 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 7 ways as a sum of consecutive naturals, for example, 1391 + ... + 1791.

It is an arithmetic number, because the mean of its divisors is an integer number (84018).

2⁶³⁷⁹⁹¹ is an apocalyptic number.

637991 is a deficient number, since it is larger than the sum of its proper divisors (34153).

637991 is a wasteful number, since it uses less digits than its factorization.

637991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 481.

The product of its digits is 10206, while the sum is 35.

The square root of 637991 is about 798.7433880791. The cubic root of 637991 is about 86.0871210159.

The spelling of 637991 in words is "six hundred thirty-seven thousand, nine hundred ninety-one".