51781 has 4 divisors (see below), whose sum is σ = 52812. Its totient is φ = 50752.

The previous prime is 51769. The next prime is 51787. The reversal of 51781 is 18715.

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 43681 + 8100 = 209^2 + 90^2 .

It is a cyclic number.

It is not a de Polignac number, because 51781 - 2⁵ = 51749 is a prime.

It is a super-2 number, since 2×51781² = 5362543922, 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 (51787) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 436 + ... + 541.

It is an arithmetic number, because the mean of its divisors is an integer number (13203).

2⁵¹⁷⁸¹ is an apocalyptic number.

It is an amenable number.

51781 is a deficient number, since it is larger than the sum of its proper divisors (1031).

51781 is an equidigital number, since it uses as much as digits as its factorization.

51781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1030.

The product of its digits is 280, while the sum is 22.

The square root of 51781 is about 227.5543891029. The cubic root of 51781 is about 37.2726391215.

The spelling of 51781 in words is "fifty-one thousand, seven hundred eighty-one".