51686821 has 4 divisors (see below), whose sum is σ = 54407200. Its totient is φ = 48966444.

The previous prime is 51686779. The next prime is 51686849. The reversal of 51686821 is 12868615.

51686821 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, 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 51686821 - 2⁹ = 51686309 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (51687821) 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, 1360161 + ... + 1360198.

It is an arithmetic number, because the mean of its divisors is an integer number (13601800).

Almost surely, 2^51686821 is an apocalyptic number.

It is an amenable number.

51686821 is a deficient number, since it is larger than the sum of its proper divisors (2720379).

51686821 is a wasteful number, since it uses less digits than its factorization.

51686821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2720378.

The product of its digits is 23040, while the sum is 37.

The square root of 51686821 is about 7189.3546998322. The cubic root of 51686821 is about 372.5002831702.

The spelling of 51686821 in words is "fifty-one million, six hundred eighty-six thousand, eight hundred twenty-one".