821693491 has 4 divisors (see below), whose sum is σ = 821816800. Its totient is φ = 821570184.

The previous prime is 821693459. The next prime is 821693497. The reversal of 821693491 is 194396128.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 821693491 - 2⁵ = 821693459 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (821693497) 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, 51051 + ... + 65188.

It is an arithmetic number, because the mean of its divisors is an integer number (205454200).

Almost surely, 2^821693491 is an apocalyptic number.

821693491 is a deficient number, since it is larger than the sum of its proper divisors (123309).

821693491 is a wasteful number, since it uses less digits than its factorization.

821693491 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 123308.

The product of its digits is 93312, while the sum is 43.

The square root of 821693491 is about 28665.1965107515. The cubic root of 821693491 is about 936.6340651484.

The spelling of 821693491 in words is "eight hundred twenty-one million, six hundred ninety-three thousand, four hundred ninety-one".