820587991 has 4 divisors (see below), whose sum is σ = 820921752. Its totient is φ = 820254232.

The previous prime is 820587983. The next prime is 820588001. The reversal of 820587991 is 199785028.

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 820587991 - 2³ = 820587983 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 (820587091) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 163165 + ... + 168118.

It is an arithmetic number, because the mean of its divisors is an integer number (205230438).

Almost surely, 2^820587991 is an apocalyptic number.

820587991 is a deficient number, since it is larger than the sum of its proper divisors (333761).

820587991 is a wasteful number, since it uses less digits than its factorization.

820587991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 333760.

The product of its (nonzero) digits is 362880, while the sum is 49.

The square root of 820587991 is about 28645.9070549354. The cubic root of 820587991 is about 936.2138299149.

The spelling of 820587991 in words is "eight hundred twenty million, five hundred eighty-seven thousand, nine hundred ninety-one".