661857 has 8 divisors (see below), whose sum is σ = 1008576. Its totient is φ = 378192.

The previous prime is 661849. The next prime is 661873. The reversal of 661857 is 758166.

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

It is not a de Polignac number, because 661857 - 2³ = 661849 is a prime.

It is not an unprimeable number, because it can be changed into a prime (661877) 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, 15738 + ... + 15779.

It is an arithmetic number, because the mean of its divisors is an integer number (126072).

2⁶⁶¹⁸⁵⁷ is an apocalyptic number.

It is an amenable number.

661857 is a deficient number, since it is larger than the sum of its proper divisors (346719).

661857 is a wasteful number, since it uses less digits than its factorization.

661857 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 31527.

The product of its digits is 10080, while the sum is 33.

The square root of 661857 is about 813.5459421569. The cubic root of 661857 is about 87.1474576857.

The spelling of 661857 in words is "six hundred sixty-one thousand, eight hundred fifty-seven".