It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 16621 = 11 ⋅1511.
It is a cyclic number.
It is a Duffinian number.
It is a plaindrome in base 13.
It is a congruent number.
212661 is an apocalyptic number.
12661 is a gapful number since it is divisible by the number (11) formed by its first and last digit.
It is an amenable number.
12661 is a wasteful number, since it uses less digits than its factorization.
12661 is an evil number, because the sum of its binary digits is even.
The sum of its prime factors is 1162.
The square root of 12661 is about 112.5211091307. The cubic root of 12661 is about 23.3071588580.
The spelling of 12661 in words is "twelve thousand, six hundred sixty-one".