820991 has 2 divisors, whose sum is σ = 820992. Its totient is φ = 820990.

The previous prime is 820969. The next prime is 820997. The reversal of 820991 is 199028.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 820991 - 2⁶ = 820927 is a prime.

It is a Chen prime.

It is an Ulam number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (820997) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 410495 + 410496.

It is an arithmetic number, because the mean of its divisors is an integer number (410496).

2⁸²⁰⁹⁹¹ is an apocalyptic number.

820991 is a deficient number, since it is larger than the sum of its proper divisors (1).

820991 is an equidigital number, since it uses as much as digits as its factorization.

820991 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1296, while the sum is 29.

The square root of 820991 is about 906.0855368010. The cubic root of 820991 is about 93.6367069971.

The spelling of 820991 in words is "eight hundred twenty thousand, nine hundred ninety-one".