691781 has 4 divisors (see below), whose sum is σ = 732492. Its totient is φ = 651072.

The previous prime is 691763. The next prime is 691787. The reversal of 691781 is 187196.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 410881 + 280900 = 641^2 + 530^2 .

It is a cyclic number.

It is not a de Polignac number, because 691781 - 2¹⁰ = 690757 is a prime.

It is a super-2 number, since 2×691781² = 957121903922, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 691781.

It is not an unprimeable number, because it can be changed into a prime (691787) 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, 20330 + ... + 20363.

It is an arithmetic number, because the mean of its divisors is an integer number (183123).

2⁶⁹¹⁷⁸¹ is an apocalyptic number.

It is an amenable number.

691781 is a deficient number, since it is larger than the sum of its proper divisors (40711).

691781 is a wasteful number, since it uses less digits than its factorization.

691781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 40710.

The product of its digits is 3024, while the sum is 32.

The square root of 691781 is about 831.7337314309. The cubic root of 691781 is about 88.4415224356.

The spelling of 691781 in words is "six hundred ninety-one thousand, seven hundred eighty-one".