51684721 has 4 divisors (see below), whose sum is σ = 56383344. Its totient is φ = 46986100.

The previous prime is 51684713. The next prime is 51684761. The reversal of 51684721 is 12748615.

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 51684721 - 2³ = 51684713 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (51684761) 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, 2349295 + ... + 2349316.

It is an arithmetic number, because the mean of its divisors is an integer number (14095836).

Almost surely, 2^51684721 is an apocalyptic number.

It is an amenable number.

51684721 is a deficient number, since it is larger than the sum of its proper divisors (4698623).

51684721 is a wasteful number, since it uses less digits than its factorization.

51684721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4698622.

The product of its digits is 13440, while the sum is 34.

The square root of 51684721 is about 7189.2086490795. The cubic root of 51684721 is about 372.4952382918.

It can be divided in two parts, 5168 and 4721, that added together give a palindrome (9889).

The spelling of 51684721 in words is "fifty-one million, six hundred eighty-four thousand, seven hundred twenty-one".