811511661 has 4 divisors (see below), whose sum is σ = 1082015552. Its totient is φ = 541007772.

The previous prime is 811511629. The next prime is 811511689. The reversal of 811511661 is 166115118.

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.

It is not a de Polignac number, because 811511661 - 2⁵ = 811511629 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (811511161) 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, 135251941 + ... + 135251946.

It is an arithmetic number, because the mean of its divisors is an integer number (270503888).

Almost surely, 2^811511661 is an apocalyptic number.

It is an amenable number.

811511661 is a deficient number, since it is larger than the sum of its proper divisors (270503891).

811511661 is a wasteful number, since it uses less digits than its factorization.

811511661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 270503890.

The product of its digits is 1440, while the sum is 30.

The square root of 811511661 is about 28487.0437392159. The cubic root of 811511661 is about 932.7492781132.

Adding to 811511661 its reverse (166115118), we get a palindrome (977626779).

The spelling of 811511661 in words is "eight hundred eleven million, five hundred eleven thousand, six hundred sixty-one".