856521551 has 4 divisors (see below), whose sum is σ = 856650600. Its totient is φ = 856392504.

The previous prime is 856521521. The next prime is 856521563. The reversal of 856521551 is 155125658.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 155125658 = 2 ⋅77562829.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-856521551 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 (856521521) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 53996 + ... + 68033.

It is an arithmetic number, because the mean of its divisors is an integer number (214162650).

Almost surely, 2^856521551 is an apocalyptic number.

856521551 is a deficient number, since it is larger than the sum of its proper divisors (129049).

856521551 is a wasteful number, since it uses less digits than its factorization.

856521551 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 129048.

The product of its digits is 60000, while the sum is 38.

The square root of 856521551 is about 29266.3894424987. The cubic root of 856521551 is about 949.6846787306.

The spelling of 856521551 in words is "eight hundred fifty-six million, five hundred twenty-one thousand, five hundred fifty-one".