820664891 has 16 divisors (see below), whose sum is σ = 893276160. Its totient is φ = 751083840.

The previous prime is 820664869. The next prime is 820664893. The reversal of 820664891 is 198466028.

It is a happy number.

It is a cyclic number.

It is not a de Polignac number, because 820664891 - 2¹⁸ = 820402747 is a prime.

It is not an unprimeable number, because it can be changed into a prime (820664893) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 551150 + ... + 552636.

It is an arithmetic number, because the mean of its divisors is an integer number (55829760).

Almost surely, 2^820664891 is an apocalyptic number.

820664891 is a deficient number, since it is larger than the sum of its proper divisors (72611269).

820664891 is a wasteful number, since it uses less digits than its factorization.

820664891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2474.

The product of its (nonzero) digits is 165888, while the sum is 44.

The square root of 820664891 is about 28647.2492745813. The cubic root of 820664891 is about 936.2430742273.

The spelling of 820664891 in words is "eight hundred twenty million, six hundred sixty-four thousand, eight hundred ninety-one".