865521891 has 48 divisors (see below), whose sum is σ = 1401487360. Its totient is φ = 511116480.

The previous prime is 865521889. The next prime is 865521949. The reversal of 865521891 is 198125568.

It is a happy number.

865521891 is a `hidden beast` number, since 8 + 6 + 552 + 1 + 8 + 91 = 666.

It is not a de Polignac number, because 865521891 - 2¹ = 865521889 is a prime.

It is not an unprimeable number, because it can be changed into a prime (865521821) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 459690 + ... + 461568.

Almost surely, 2^865521891 is an apocalyptic number.

865521891 is a deficient number, since it is larger than the sum of its proper divisors (535965469).

865521891 is a wasteful number, since it uses less digits than its factorization.

865521891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2056 (or 2053 counting only the distinct ones).

The product of its digits is 172800, while the sum is 45.

The square root of 865521891 is about 29419.7534150101. The cubic root of 865521891 is about 952.9995280086. Note that the first 3 decimals are identical.

The spelling of 865521891 in words is "eight hundred sixty-five million, five hundred twenty-one thousand, eight hundred ninety-one".