691391 has 4 divisors (see below), whose sum is σ = 727800. Its totient is φ = 654984.

The previous prime is 691381. The next prime is 691399. The reversal of 691391 is 193196.

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

It is a cyclic number.

It is not a de Polignac number, because 691391 - 2¹⁰ = 690367 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (691399) 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, 18176 + ... + 18213.

It is an arithmetic number, because the mean of its divisors is an integer number (181950).

2⁶⁹¹³⁹¹ is an apocalyptic number.

691391 is a deficient number, since it is larger than the sum of its proper divisors (36409).

691391 is a wasteful number, since it uses less digits than its factorization.

691391 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 36408.

The product of its digits is 1458, while the sum is 29.

The square root of 691391 is about 831.4992483460. The cubic root of 691391 is about 88.4248993147.

The spelling of 691391 in words is "six hundred ninety-one thousand, three hundred ninety-one".