631691991 has 48 divisors (see below), whose sum is σ = 1082984448. Its totient is φ = 347198400.

The previous prime is 631691969. The next prime is 631691999. The reversal of 631691991 is 199196136.

631691991 is a `hidden beast` number, since 631 + 6 + 9 + 1 + 9 + 9 + 1 = 666.

It is not a de Polignac number, because 631691991 - 2⁵ = 631691959 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (631691999) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 352600 + ... + 354386.

It is an arithmetic number, because the mean of its divisors is an integer number (22562176).

Almost surely, 2^631691991 is an apocalyptic number.

631691991 is a deficient number, since it is larger than the sum of its proper divisors (451292457).

631691991 is a wasteful number, since it uses less digits than its factorization.

631691991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2012 (or 2009 counting only the distinct ones).

The product of its digits is 78732, while the sum is 45.

The square root of 631691991 is about 25133.4834633005. The cubic root of 631691991 is about 858.0286516261.

The spelling of 631691991 in words is "six hundred thirty-one million, six hundred ninety-one thousand, nine hundred ninety-one".