51721 has 2 divisors, whose sum is σ = 51722. Its totient is φ = 51720.

The previous prime is 51719. The next prime is 51749. The reversal of 51721 is 12715.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 32400 + 19321 = 180^2 + 139^2 .

It is a cyclic number.

It is not a de Polignac number, because 51721 - 2¹ = 51719 is a prime.

Together with 51719, it forms a pair of twin primes.

It is a junction number, because it is equal to n+sod(n) for n = 51695 and 51704.

It is not a weakly prime, because it can be changed into another prime (51421) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 25860 + 25861.

It is an arithmetic number, because the mean of its divisors is an integer number (25861).

2⁵¹⁷²¹ is an apocalyptic number.

It is an amenable number.

51721 is a deficient number, since it is larger than the sum of its proper divisors (1).

51721 is an equidigital number, since it uses as much as digits as its factorization.

51721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 70, while the sum is 16.

The square root of 51721 is about 227.4225142768. The cubic root of 51721 is about 37.2582372967.

The spelling of 51721 in words is "fifty-one thousand, seven hundred twenty-one".