691123681 has 2 divisors, whose sum is σ = 691123682. Its totient is φ = 691123680.

The previous prime is 691123669. The next prime is 691123687. The reversal of 691123681 is 186321196.

691123681 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 588790225 + 102333456 = 24265^2 + 10116^2 .

It is a cyclic number.

It is not a de Polignac number, because 691123681 - 2¹⁷ = 690992609 is a prime.

It is a super-2 number, since 2×691123681² = 955303884877979522, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 691123681.

It is not a weakly prime, because it can be changed into another prime (691123687) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 345561840 + 345561841.

It is an arithmetic number, because the mean of its divisors is an integer number (345561841).

Almost surely, 2^691123681 is an apocalyptic number.

It is an amenable number.

691123681 is a deficient number, since it is larger than the sum of its proper divisors (1).

691123681 is an equidigital number, since it uses as much as digits as its factorization.

691123681 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 15552, while the sum is 37.

The square root of 691123681 is about 26289.2312744211. The cubic root of 691123681 is about 884.1350166241.

The spelling of 691123681 in words is "six hundred ninety-one million, one hundred twenty-three thousand, six hundred eighty-one".