Subtracting from 2661 its reverse (1662), we obtain a palindrome (999).
2661 is nontrivially palindromic in base 2.
2661 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.
It is a semiprime because it is the product of two primes.
It is a cyclic number.
It is a D-number.
It is a Curzon number.
2661 is a lucky number.
It is a plaindrome in base 11 and base 13.
It is a nialpdrome in base 14 and base 16.
It is a self number, because there is not a number n which added to its sum of digits gives 2661.
It is a congruent number.
It is an amenable number.
2661 is an equidigital number, since it uses as much as digits as its factorization.
2661 is an evil number, because the sum of its binary digits is even.
The sum of its prime factors is 890.
The square root of 2661 is about 51.5848815061. The cubic root of 2661 is about 13.8573959030.
The spelling of 2661 in words is "two thousand, six hundred sixty-one".