51681991 has 16 divisors (see below), whose sum is σ = 54835200. Its totient is φ = 48644640.

The previous prime is 51681979. The next prime is 51682027. The reversal of 51681991 is 19918615.

51681991 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a cyclic number.

It is not a de Polignac number, because 51681991 - 2⁷ = 51681863 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 (51681911) 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 15 ways as a sum of consecutive naturals, for example, 309390 + ... + 309556.

It is an arithmetic number, because the mean of its divisors is an integer number (3427200).

Almost surely, 2^51681991 is an apocalyptic number.

51681991 is a deficient number, since it is larger than the sum of its proper divisors (3153209).

51681991 is a wasteful number, since it uses less digits than its factorization.

51681991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 414.

The product of its digits is 19440, while the sum is 40.

The square root of 51681991 is about 7189.0187786651. The cubic root of 51681991 is about 372.4886797455.

The spelling of 51681991 in words is "fifty-one million, six hundred eighty-one thousand, nine hundred ninety-one".