861661 has 4 divisors (see below), whose sum is σ = 868000. Its totient is φ = 855324.

The previous prime is 861659. The next prime is 861691. The reversal of 861661 is 166168.

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 a cyclic number.

It is not a de Polignac number, because 861661 - 2¹ = 861659 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 (861691) 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, 2961 + ... + 3238.

It is an arithmetic number, because the mean of its divisors is an integer number (217000).

2⁸⁶¹⁶⁶¹ is an apocalyptic number.

It is an amenable number.

861661 is a deficient number, since it is larger than the sum of its proper divisors (6339).

861661 is a wasteful number, since it uses less digits than its factorization.

861661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6338.

The product of its digits is 1728, while the sum is 28.

The square root of 861661 is about 928.2569687323. The cubic root of 861661 is about 95.1580379647.

The spelling of 861661 in words is "eight hundred sixty-one thousand, six hundred sixty-one".