691875981 has 6 divisors (see below), whose sum is σ = 999376430. Its totient is φ = 461250648.

The previous prime is 691875973. The next prime is 691876001. The reversal of 691875981 is 189578196.

It can be written as a sum of positive squares in only one way, i.e., 689535081 + 2340900 = 26259^2 + 1530^2 .

It is not a de Polignac number, because 691875981 - 2³ = 691875973 is a prime.

It is a super-2 number, since 2×691875981² = 957384746169424722, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (691875931) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 38437546 + ... + 38437563.

Almost surely, 2^691875981 is an apocalyptic number.

It is an amenable number.

691875981 is a deficient number, since it is larger than the sum of its proper divisors (307500449).

691875981 is a wasteful number, since it uses less digits than its factorization.

691875981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 76875115 (or 76875112 counting only the distinct ones).

The product of its digits is 1088640, while the sum is 54.

The square root of 691875981 is about 26303.5355228152. The cubic root of 691875981 is about 884.4556990143.

The spelling of 691875981 in words is "six hundred ninety-one million, eight hundred seventy-five thousand, nine hundred eighty-one".