2491 has 4 divisors (see below), whose sum is σ = 2592. Its totient is φ = 2392.

The previous prime is 2477. The next prime is 2503. The reversal of 2491 is 1942.

2491 is an esthetic number in base 4, because in such base its adjacent digits differ by 1.

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, and also an emirpimes, since its reverse is a distinct semiprime: 1942 = 2 ⋅971.

It is a cyclic number.

It is not a de Polignac number, because 2491 - 2^{5} = 2459 is a prime.

It is a Duffinian number.

2491 is a lucky number.

It is a plaindrome in base 9 and base 16.

It is a nialpdrome in base 15.

It is not an unprimeable number, because it can be changed into a prime (2411) 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, 21 + ... + 73.

It is an arithmetic number, because the mean of its divisors is an integer number (648).

2^{2491} is an apocalyptic number.

2491 is a deficient number, since it is larger than the sum of its proper divisors (101).

2491 is an equidigital number, since it uses as much as digits as its factorization.

With its successor (2492) it forms a Ruth-Aaron pair, since the sum of their prime factors is the same (100).

2491 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 100.

The product of its digits is 72, while the sum is 16.

The square root of 2491 is about 49.9099188539. The cubic root of 2491 is about 13.5557819943. Note that the first 3 decimals are identical.

The spelling of 2491 in words is "two thousand, four hundred ninety-one".

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