813661 has 4 divisors (see below), whose sum is σ = 816732. Its totient is φ = 810592.

The previous prime is 813647. The next prime is 813677. The reversal of 813661 is 166318.

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 476100 + 337561 = 690^2 + 581^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-813661 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 (813601) 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 in 3 ways as a sum of consecutive naturals, for example, 1096 + ... + 1681.

It is an arithmetic number, because the mean of its divisors is an integer number (204183).

2⁸¹³⁶⁶¹ is an apocalyptic number.

It is an amenable number.

813661 is a deficient number, since it is larger than the sum of its proper divisors (3071).

813661 is a wasteful number, since it uses less digits than its factorization.

813661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3070.

The product of its digits is 864, while the sum is 25.

The square root of 813661 is about 902.0315958989. The cubic root of 813661 is about 93.3572033618.

Adding to 813661 its reverse (166318), we get a palindrome (979979).

The spelling of 813661 in words is "eight hundred thirteen thousand, six hundred sixty-one".