51639920 has 20 divisors (see below), whose sum is σ = 120063000. Its totient is φ = 20655936.

The previous prime is 51639919. The next prime is 51639961. The reversal of 51639920 is 2993615.

It is a tau number, because it is divible by the number of its divisors (20).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 322670 + ... + 322829.

It is an arithmetic number, because the mean of its divisors is an integer number (6003150).

Almost surely, 2^51639920 is an apocalyptic number.

It is an amenable number.

51639920 is an abundant number, since it is smaller than the sum of its proper divisors (68423080).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

51639920 is a wasteful number, since it uses less digits than its factorization.

51639920 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 645512 (or 645506 counting only the distinct ones).

The product of its (nonzero) digits is 14580, while the sum is 35.

The square root of 51639920 is about 7186.0921229831. The cubic root of 51639920 is about 372.3875792453.

The spelling of 51639920 in words is "fifty-one million, six hundred thirty-nine thousand, nine hundred twenty".