399561 has 4 divisors (see below), whose sum is σ = 532752. Its totient is φ = 266372.

The previous prime is 399557. The next prime is 399571. The reversal of 399561 is 165993.

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: 165993 = 3 ⋅55331.

It is a cyclic number.

It is not a de Polignac number, because 399561 - 2² = 399557 is a prime.

It is a D-number.

It is not an unprimeable number, because it can be changed into a prime (399541) 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, 66591 + ... + 66596.

It is an arithmetic number, because the mean of its divisors is an integer number (133188).

2³⁹⁹⁵⁶¹ is an apocalyptic number.

It is an amenable number.

399561 is a deficient number, since it is larger than the sum of its proper divisors (133191).

399561 is a wasteful number, since it uses less digits than its factorization.

399561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 133190.

The product of its digits is 7290, while the sum is 33.

The square root of 399561 is about 632.1083767836. The cubic root of 399561 is about 73.6536652754.

The spelling of 399561 in words is "three hundred ninety-nine thousand, five hundred sixty-one".