399661 has 4 divisors (see below), whose sum is σ = 404800. Its totient is φ = 394524.

The previous prime is 399647. The next prime is 399667. The reversal of 399661 is 166993.

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, and also an emirpimes, since its reverse is a distinct semiprime: 166993 = 41 ⋅4073.

It is a cyclic number.

It is not a de Polignac number, because 399661 - 2⁹ = 399149 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 (399667) 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, 2451 + ... + 2608.

It is an arithmetic number, because the mean of its divisors is an integer number (101200).

2³⁹⁹⁶⁶¹ is an apocalyptic number.

It is an amenable number.

399661 is a deficient number, since it is larger than the sum of its proper divisors (5139).

399661 is an equidigital number, since it uses as much as digits as its factorization.

399661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5138.

The product of its digits is 8748, while the sum is 34.

The square root of 399661 is about 632.1874721948. The cubic root of 399661 is about 73.6598093119.

The spelling of 399661 in words is "three hundred ninety-nine thousand, six hundred sixty-one".