51821865684 has 18 divisors (see below), whose sum is σ = 130994160570. Its totient is φ = 17273955216.

The previous prime is 51821865677. The next prime is 51821865707. The reversal of 51821865684 is 48656812815.

51821865684 is a `hidden beast` number, since 51 + 8 + 21 + 8 + 6 + 568 + 4 = 666.

It can be written as a sum of positive squares in only one way, i.e., 50126732100 + 1695133584 = 223890^2 + 41172^2 .

It is a tau number, because it is divible by the number of its divisors (18).

It is a self number, because there is not a number n which added to its sum of digits gives 51821865684.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 719748099 + ... + 719748170.

It is an arithmetic number, because the mean of its divisors is an integer number (7277453365).

Almost surely, 2^51821865684 is an apocalyptic number.

It is an amenable number.

51821865684 is an abundant number, since it is smaller than the sum of its proper divisors (79172294886).

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

51821865684 is a wasteful number, since it uses less digits than its factorization.

51821865684 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1439496279 (or 1439496274 counting only the distinct ones).

The product of its digits is 3686400, while the sum is 54.

The spelling of 51821865684 in words is "fifty-one billion, eight hundred twenty-one million, eight hundred sixty-five thousand, six hundred eighty-four".