4991 has 8 divisors (see below), whose sum is σ = 6144.
Its totient is φ = 3960.
The previous prime is 4987. The next prime is 4993. The reversal of 4991 is 1994.
It is a sphenic number, since it is the product of 3 distinct primes.
It is a cyclic number.
It is not a de Polignac number, because 4991 - 22 = 4987 is a prime.
It is a Harshad number since it is a multiple of its sum of digits (23).
It is a Duffinian number.
It is a plaindrome in base 8, base 13 and base 16.
It is a congruent number.
It is not an unprimeable number, because it can be changed into a prime (4993) by changing a digit.
It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 146 + ... + 176.
It is an arithmetic number, because the mean of its divisors is an integer number (768).
24991 is an apocalyptic number.
4991 is a deficient number, since it is larger than the sum of its proper divisors (1153).
4991 is a wasteful number, since it uses less digits than its factorization.
4991 is an evil number, because the sum of its binary digits is even.
The sum of its prime factors is 61.
The product of its digits is 324, while the sum is 23.
The square root of 4991 is about 70.6470098447.
The cubic root of 4991 is about 17.0894934490.
The spelling of 4991 in words is "four thousand, nine hundred ninety-one".