691891 has 2 divisors, whose sum is σ = 691892. Its totient is φ = 691890.

The previous prime is 691877. The next prime is 691897. The reversal of 691891 is 198196.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 691891 - 2⁷ = 691763 is a prime.

It is not a weakly prime, because it can be changed into another prime (691897) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 345945 + 345946.

It is an arithmetic number, because the mean of its divisors is an integer number (345946).

2⁶⁹¹⁸⁹¹ is an apocalyptic number.

691891 is a deficient number, since it is larger than the sum of its proper divisors (1).

691891 is an equidigital number, since it uses as much as digits as its factorization.

691891 is an odious number, because the sum of its binary digits is odd.

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

The square root of 691891 is about 831.7998557345. The cubic root of 691891 is about 88.4462098786.

The spelling of 691891 in words is "six hundred ninety-one thousand, eight hundred ninety-one".