811681 has 8 divisors (see below), whose sum is σ = 904680. Its totient is φ = 723072.

The previous prime is 811667. The next prime is 811691. The reversal of 811681 is 186118.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 1681 + 810000 = 41^2 + 900^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 811681 - 2⁵ = 811649 is a prime.

It is a super-2 number, since 2×811681² = 1317652091522, which contains 22 as substring.

It is an Ulam number.

It is a Duffinian number.

811681 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (811651) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 700 + ... + 1453.

It is an arithmetic number, because the mean of its divisors is an integer number (113085).

2⁸¹¹⁶⁸¹ is an apocalyptic number.

It is an amenable number.

811681 is a deficient number, since it is larger than the sum of its proper divisors (92999).

811681 is a wasteful number, since it uses less digits than its factorization.

811681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2195.

The product of its digits is 384, while the sum is 25.

The square root of 811681 is about 900.9334048641. The cubic root of 811681 is about 93.2814152862.

Adding to 811681 its reverse (186118), we get a palindrome (997799).

It can be divided in two parts, 81 and 1681, that multiplied together give a square (136161 = 369²).

The spelling of 811681 in words is "eight hundred eleven thousand, six hundred eighty-one".