813756661 has 4 divisors (see below), whose sum is σ = 814012524. Its totient is φ = 813500800.

The previous prime is 813756649. The next prime is 813756679. The reversal of 813756661 is 166657318.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 166657318 = 2 ⋅83328659.

It can be written as a sum of positive squares in 2 ways, for example, as 265494436 + 548262225 = 16294^2 + 23415^2 .

It is a cyclic number.

It is not a de Polignac number, because 813756661 - 2¹⁹ = 813232373 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 (813756641) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 123100 + ... + 129541.

It is an arithmetic number, because the mean of its divisors is an integer number (203503131).

Almost surely, 2^813756661 is an apocalyptic number.

It is an amenable number.

813756661 is a deficient number, since it is larger than the sum of its proper divisors (255863).

813756661 is a wasteful number, since it uses less digits than its factorization.

813756661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 255862.

The product of its digits is 181440, while the sum is 43.

The square root of 813756661 is about 28526.4204028476. The cubic root of 813756661 is about 933.6086184428.

The spelling of 813756661 in words is "eight hundred thirteen million, seven hundred fifty-six thousand, six hundred sixty-one".