821664903891 has 32 divisors (see below), whose sum is σ = 1216076843520. Its totient is φ = 490275765504.

The previous prime is 821664903869. The next prime is 821664903901. The reversal of 821664903891 is 198309466128.

It is not a de Polignac number, because 821664903891 - 2¹¹ = 821664901843 is a prime.

It is not an unprimeable number, because it can be changed into a prime (821664903811) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 1558431 + ... + 2017928.

It is an arithmetic number, because the mean of its divisors is an integer number (38002401360).

Almost surely, 2^821664903891 is an apocalyptic number.

821664903891 is a deficient number, since it is larger than the sum of its proper divisors (394411939629).

821664903891 is a wasteful number, since it uses less digits than its factorization.

821664903891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3576555.

The product of its (nonzero) digits is 4478976, while the sum is 57.

The spelling of 821664903891 in words is "eight hundred twenty-one billion, six hundred sixty-four million, nine hundred three thousand, eight hundred ninety-one".