661811 has 4 divisors (see below), whose sum is σ = 674352. Its totient is φ = 649272.

The previous prime is 661777. The next prime is 661823. The reversal of 661811 is 118166.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 118166 = 2 ⋅59083.

It is a cyclic number.

It is not a de Polignac number, because 661811 - 2¹⁰ = 660787 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (660811) 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, 6191 + ... + 6296.

It is an arithmetic number, because the mean of its divisors is an integer number (168588).

2⁶⁶¹⁸¹¹ is an apocalyptic number.

661811 is a deficient number, since it is larger than the sum of its proper divisors (12541).

661811 is a wasteful number, since it uses less digits than its factorization.

661811 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12540.

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

The square root of 661811 is about 813.5176703674. The cubic root of 661811 is about 87.1454386817.

Adding to 661811 its reverse (118166), we get a palindrome (779977).

The spelling of 661811 in words is "six hundred sixty-one thousand, eight hundred eleven".