51665 has 4 divisors (see below), whose sum is σ = 62004. Its totient is φ = 41328.

The previous prime is 51659. The next prime is 51673. The reversal of 51665 is 56615.

51665 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 can be written as a sum of positive squares in 2 ways, for example, as 28561 + 23104 = 169^2 + 152^2 .

It is a cyclic number.

It is not a de Polignac number, because 51665 - 2¹² = 47569 is a prime.

It is a Duffinian number.

It is a nialpdrome in base 9.

It is a self number, because there is not a number n which added to its sum of digits gives 51665.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 5162 + ... + 5171.

It is an arithmetic number, because the mean of its divisors is an integer number (15501).

2⁵¹⁶⁶⁵ is an apocalyptic number.

It is an amenable number.

51665 is a deficient number, since it is larger than the sum of its proper divisors (10339).

51665 is a wasteful number, since it uses less digits than its factorization.

51665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10338.

The product of its digits is 900, while the sum is 23.

The square root of 51665 is about 227.2993620757. The cubic root of 51665 is about 37.2447855410.

Subtracting 51665 from its reverse (56615), we obtain a triangular number (4950 = T₉₉).

The spelling of 51665 in words is "fifty-one thousand, six hundred sixty-five".