7999 has 4 divisors (see below), whose sum is σ = 8440. Its totient is φ = 7560.

The previous prime is 7993. The next prime is 8009. The reversal of 7999 is 9997.

7999 = T₁₉ + T₂₀ + ... + T₃₇.

It is a Cunningham number, because it is equal to 20³-1.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 9997 = 13 ⋅769.

It is a cyclic number.

It is not a de Polignac number, because 7999 - 2⁹ = 7487 is a prime.

It is a Duffinian number.

7999 is a modest number, since divided by 99 gives 79 as remainder.

It is a plaindrome in base 5 and base 10.

It is a zygodrome in base 2.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (7993) 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 in 3 ways as a sum of consecutive naturals, for example, 192 + ... + 229.

It is an arithmetic number, because the mean of its divisors is an integer number (2110).

2⁷⁹⁹⁹ is an apocalyptic number.

7999 is a deficient number, since it is larger than the sum of its proper divisors (441).

7999 is a wasteful number, since it uses less digits than its factorization.

7999 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 440.

The product of its digits is 5103, while the sum is 34.

The square root of 7999 is about 89.4371287553. The cubic root of 7999 is about 19.9991666319. Note that the first 3 decimals are identical.

It can be divided in two parts, 799 and 9, that added together give a palindrome (808).

The spelling of 7999 in words is "seven thousand, nine hundred ninety-nine".