865564821 has 12 divisors (see below), whose sum is σ = 1363920480. Its totient is φ = 524584680.

The previous prime is 865564793. The next prime is 865564859. The reversal of 865564821 is 128465568.

865564821 is a `hidden beast` number, since 8 + 6 + 5 + 564 + 82 + 1 = 666.

It is not a de Polignac number, because 865564821 - 2⁶ = 865564757 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (865564121) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 4371441 + ... + 4371638.

It is an arithmetic number, because the mean of its divisors is an integer number (113660040).

Almost surely, 2^865564821 is an apocalyptic number.

It is an amenable number.

865564821 is a deficient number, since it is larger than the sum of its proper divisors (498355659).

865564821 is a wasteful number, since it uses less digits than its factorization.

865564821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8743096 (or 8743093 counting only the distinct ones).

The product of its digits is 460800, while the sum is 45.

The square root of 865564821 is about 29420.4830177888. The cubic root of 865564821 is about 953.0152840488.

The spelling of 865564821 in words is "eight hundred sixty-five million, five hundred sixty-four thousand, eight hundred twenty-one".