12991 has 4 divisors (see below), whose sum is σ = 14184. Its totient is φ = 11800.
The previous prime is 12983. The next prime is 13001. The reversal of 12991 is 19921.
12991 = T43 + T44 + ... + T53.
12991 = 442 + 452 + ... + 492.
It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 19921 = 11 ⋅1811.
It is a cyclic number.
It is not a de Polignac number, because 12991 - 23 = 12983 is a prime.
It is a Duffinian number.
12991 is a lucky number.
It is a nialpdrome in base 11.
It is a congruent number.
It is not an unprimeable number, because it can be changed into a prime (12911) 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, 580 + ... + 601.
It is an arithmetic number, because the mean of its divisors is an integer number (3546).
212991 is an apocalyptic number.
12991 is a gapful number since it is divisible by the number (11) formed by its first and last digit.
12991 is a deficient number, since it is larger than the sum of its proper divisors (1193).
12991 is a wasteful number, since it uses less digits than its factorization.
12991 is an evil number, because the sum of its binary digits is even.
The sum of its prime factors is 1192.
The product of its digits is 162, while the sum is 22.
The square root of 12991 is about 113.9780680657. The cubic root of 12991 is about 23.5079194676.
It can be divided in two parts, 1 and 2991, that added together give a palindrome (2992).
The spelling of 12991 in words is "twelve thousand, nine hundred ninety-one".
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