691981 has 4 divisors (see below), whose sum is σ = 706752. Its totient is φ = 677212.

The previous prime is 691979. The next prime is 691991. The reversal of 691981 is 189196.

691981 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 691981 - 2¹ = 691979 is a prime.

It is a super-2 number, since 2×691981² = 957675408722, 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 (691921) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 7315 + ... + 7408.

It is an arithmetic number, because the mean of its divisors is an integer number (176688).

2⁶⁹¹⁹⁸¹ is an apocalyptic number.

It is an amenable number.

691981 is a deficient number, since it is larger than the sum of its proper divisors (14771).

691981 is a wasteful number, since it uses less digits than its factorization.

691981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 14770.

The product of its digits is 3888, while the sum is 34.

The square root of 691981 is about 831.8539535279. The cubic root of 691981 is about 88.4500446896.

The spelling of 691981 in words is "six hundred ninety-one thousand, nine hundred eighty-one".