691487991 has 12 divisors (see below), whose sum is σ = 1005521400. Its totient is φ = 457897200.

The previous prime is 691487981. The next prime is 691488029. The reversal of 691487991 is 199784196.

It is not a de Polignac number, because 691487991 - 2⁵ = 691487959 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (691487981) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 256485 + ... + 259166.

It is an arithmetic number, because the mean of its divisors is an integer number (83793450).

Almost surely, 2^691487991 is an apocalyptic number.

691487991 is a deficient number, since it is larger than the sum of its proper divisors (314033409).

691487991 is a wasteful number, since it uses less digits than its factorization.

691487991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 515806 (or 515803 counting only the distinct ones).

The product of its digits is 979776, while the sum is 54.

The square root of 691487991 is about 26296.1592442699. The cubic root of 691487991 is about 884.2903398354.

The spelling of 691487991 in words is "six hundred ninety-one million, four hundred eighty-seven thousand, nine hundred ninety-one".