691777781 has 4 divisors (see below), whose sum is σ = 691891500. Its totient is φ = 691664064.

The previous prime is 691777777. The next prime is 691777829. The reversal of 691777781 is 187777196.

It is a happy number.

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 305026225 + 386751556 = 17465^2 + 19666^2 .

It is a cyclic number.

It is not a de Polignac number, because 691777781 - 2² = 691777777 is a prime.

It is a super-2 number, since 2×691777781² = 957112996570567922, 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 (691777721) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 47186 + ... + 60083.

It is an arithmetic number, because the mean of its divisors is an integer number (172972875).

Almost surely, 2^691777781 is an apocalyptic number.

It is an amenable number.

691777781 is a deficient number, since it is larger than the sum of its proper divisors (113719).

691777781 is a wasteful number, since it uses less digits than its factorization.

691777781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 113718.

The product of its digits is 1037232, while the sum is 53.

The square root of 691777781 is about 26301.6687873602. The cubic root of 691777781 is about 884.4138525652.

The spelling of 691777781 in words is "six hundred ninety-one million, seven hundred seventy-seven thousand, seven hundred eighty-one".