155999 has 4 divisors (see below), whose sum is σ = 156864. Its totient is φ = 155136.

The previous prime is 155921. The next prime is 156007. The reversal of 155999 is 999551.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 155999 - 2¹² = 151903 is a prime.

It is a Duffinian number.

155999 is a modest number, since divided by 999 gives 155 as remainder.

It is a plaindrome in base 10.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (155299) 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, 47 + ... + 560.

It is an arithmetic number, because the mean of its divisors is an integer number (39216).

2¹⁵⁵⁹⁹⁹ is an apocalyptic number.

155999 is a deficient number, since it is larger than the sum of its proper divisors (865).

155999 is an equidigital number, since it uses as much as digits as its factorization.

155999 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 864.

The product of its digits is 18225, while the sum is 38.

The square root of 155999 is about 394.9670872364. The cubic root of 155999 is about 53.8320110947.

Subtracting from 155999 its sum of digits (38), we obtain a triangular number (155961 = T₅₅₈).

The spelling of 155999 in words is "one hundred fifty-five thousand, nine hundred ninety-nine".