51981 has 4 divisors (see below), whose sum is σ = 69312. Its totient is φ = 34652.

The previous prime is 51977. The next prime is 51991. The reversal of 51981 is 18915.

51981 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, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 51981 - 2² = 51977 is a prime.

It is a super-2 number, since 2×51981² = 5404048722, which contains 22 as substring.

It is a D-number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (51941) 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, 8661 + ... + 8666.

It is an arithmetic number, because the mean of its divisors is an integer number (17328).

2⁵¹⁹⁸¹ is an apocalyptic number.

It is an amenable number.

51981 is a deficient number, since it is larger than the sum of its proper divisors (17331).

51981 is a wasteful number, since it uses less digits than its factorization.

51981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 17330.

The product of its digits is 360, while the sum is 24.

The square root of 51981 is about 227.9934209577. The cubic root of 51981 is about 37.3205650072.

The spelling of 51981 in words is "fifty-one thousand, nine hundred eighty-one".