51721805 has 4 divisors (see below), whose sum is σ = 62066172. Its totient is φ = 41377440.

The previous prime is 51721801. The next prime is 51721807. The reversal of 51721805 is 50812715.

51721805 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 29800681 + 21921124 = 5459^2 + 4682^2 .

It is not a de Polignac number, because 51721805 - 2² = 51721801 is a prime.

It is a super-2 number, since 2×51721805² = 5350290224916050, which contains 22 as substring.

It is a Duffinian 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 (51721801) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 5172176 + ... + 5172185.

It is an arithmetic number, because the mean of its divisors is an integer number (15516543).

Almost surely, 2^51721805 is an apocalyptic number.

It is an amenable number.

51721805 is a deficient number, since it is larger than the sum of its proper divisors (10344367).

51721805 is a wasteful number, since it uses less digits than its factorization.

51721805 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10344366.

The product of its (nonzero) digits is 2800, while the sum is 29.

The square root of 51721805 is about 7191.7873300036. The cubic root of 51721805 is about 372.5843059484.

It can be divided in two parts, 517 and 21805, that added together give a palindrome (22322).

The spelling of 51721805 in words is "fifty-one million, seven hundred twenty-one thousand, eight hundred five".