7981 has 4 divisors (see below), whose sum is σ = 8352.
Its totient is φ = 7612.
The previous prime is 7963. The next prime is 7993. The reversal of 7981 is 1897.
7981 = T14 + T15 + ... +
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: 1897 = 7 ⋅271.
It is a cyclic number.
It is not a de Polignac number, because 7981 - 25 = 7949 is a prime.
It is a super-2 number, since 2×79812 = 127392722, which contains 22 as substring.
It is a Duffinian number.
It is a congruent number.
It is not an unprimeable number, because it can be changed into a prime (7901) 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, 151 + ... + 196.
It is an arithmetic number, because the mean of its divisors is an integer number (2088).
7981 is the 57-th centered pentagonal number.
It is an amenable number.
7981 is a deficient number, since it is larger than the sum of its proper divisors (371).
7981 is a wasteful number, since it uses less digits than its factorization.
7981 is an odious number, because the sum of its binary digits is odd.
The sum of its prime factors is 370.
The product of its digits is 504, while the sum is 25.
The square root of 7981 is about 89.3364427320.
The cubic root of 7981 is about 19.9841541154.
Subtracting from 7981 its reverse (1897), we obtain a square (6084 = 782).
The spelling of 7981 in words is "seven thousand, nine hundred eighty-one".