405991 has 2 divisors, whose sum is σ = 405992. Its totient is φ = 405990.

The previous prime is 405989. The next prime is 405997. The reversal of 405991 is 199504.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 405991 - 2¹ = 405989 is a prime.

Together with 405989, it forms a pair of twin primes.

It is a zygodrome in base 2.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (405997) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 202995 + 202996.

It is an arithmetic number, because the mean of its divisors is an integer number (202996).

2⁴⁰⁵⁹⁹¹ is an apocalyptic number.

405991 is a deficient number, since it is larger than the sum of its proper divisors (1).

405991 is an equidigital number, since it uses as much as digits as its factorization.

405991 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1620, while the sum is 28.

The square root of 405991 is about 637.1742304896. The cubic root of 405991 is about 74.0466591543.

The spelling of 405991 in words is "four hundred five thousand, nine hundred ninety-one".