6561865728 has 560 divisors, whose sum is σ = 22836591360. Its totient is φ = 1857945600.

The previous prime is 6561865691. The next prime is 6561865733. The reversal of 6561865728 is 8275681656.

6561865728 is a `hidden beast` number, since 6 + 5 + 61 + 8 + 6 + 572 + 8 = 666.

It is a Harshad number since it is a multiple of its sum of digits (54).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 211673073 + ... + 211673103.

Almost surely, 2^6561865728 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 6561865728, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (11418295680).

6561865728 is an abundant number, since it is smaller than the sum of its proper divisors (16274725632).

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

6561865728 is a wasteful number, since it uses less digits than its factorization.

6561865728 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 109 (or 76 counting only the distinct ones).

The product of its digits is 4838400, while the sum is 54.

The square root of 6561865728 is about 81005.3438237256. The cubic root of 6561865728 is about 1872.1577776287.

The spelling of 6561865728 in words is "six billion, five hundred sixty-one million, eight hundred sixty-five thousand, seven hundred twenty-eight".