811661 has 4 divisors (see below), whose sum is σ = 854400. Its totient is φ = 768924.

The previous prime is 811651. The next prime is 811667. The reversal of 811661 is 166118.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 166118 = 2 ⋅83059.

It is a cyclic number.

It is not a de Polignac number, because 811661 - 2¹⁸ = 549517 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 811661.

It is not an unprimeable number, because it can be changed into a prime (811667) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 21341 + ... + 21378.

It is an arithmetic number, because the mean of its divisors is an integer number (213600).

2⁸¹¹⁶⁶¹ is an apocalyptic number.

It is an amenable number.

811661 is a deficient number, since it is larger than the sum of its proper divisors (42739).

811661 is a wasteful number, since it uses less digits than its factorization.

811661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 42738.

The product of its digits is 288, while the sum is 23.

The square root of 811661 is about 900.9223051962. The cubic root of 811661 is about 93.2806491216.

Adding to 811661 its reverse (166118), we get a palindrome (977779).

The spelling of 811661 in words is "eight hundred eleven thousand, six hundred sixty-one".