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 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.
22491 is an apocalyptic number.
2491 is an equidigital number, since it uses as much as digits as its factorization.
2491 is an evil number, because the sum of its binary digits is even.
The sum of its prime factors is 100.
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".