405999 has 16 divisors (see below), whose sum is σ = 656640. Its totient is φ = 245880.

The previous prime is 405997. The next prime is 406013. The reversal of 405999 is 999504.

It is not a de Polignac number, because 405999 - 2¹ = 405997 is a prime.

405999 is a modest number, since divided by 999 gives 405 as remainder.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (405991) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 387 + ... + 980.

It is an arithmetic number, because the mean of its divisors is an integer number (41040).

2⁴⁰⁵⁹⁹⁹ is an apocalyptic number.

405999 is a deficient number, since it is larger than the sum of its proper divisors (250641).

405999 is a wasteful number, since it uses less digits than its factorization.

405999 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1387 (or 1381 counting only the distinct ones).

The product of its (nonzero) digits is 14580, while the sum is 36.

The square root of 405999 is about 637.1805081765. The cubic root of 405999 is about 74.0471455111.

Subtracting 405999 from its reverse (999504), we obtain a triangular number (593505 = T₁₀₈₉).

The spelling of 405999 in words is "four hundred five thousand, nine hundred ninety-nine".