999561 has 4 divisors (see below), whose sum is σ = 1332752. Its totient is φ = 666372.

The previous prime is 999553. The next prime is 999563. The reversal of 999561 is 165999.

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: 165999 = 3 ⋅55333.

It is not a de Polignac number, because 999561 - 2³ = 999553 is a prime.

It is a D-number.

It is a Duffinian number.

999561 is a lucky number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 999561.

It is not an unprimeable number, because it can be changed into a prime (999563) 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, 166591 + ... + 166596.

It is an arithmetic number, because the mean of its divisors is an integer number (333188).

2⁹⁹⁹⁵⁶¹ is an apocalyptic number.

It is an amenable number.

999561 is a deficient number, since it is larger than the sum of its proper divisors (333191).

999561 is a wasteful number, since it uses less digits than its factorization.

999561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 333190.

The product of its digits is 21870, while the sum is 39.

The square root of 999561 is about 999.7804759046. The cubic root of 999561 is about 99.9853645248.

The spelling of 999561 in words is "nine hundred ninety-nine thousand, five hundred sixty-one".