821896991 has 2 divisors, whose sum is σ = 821896992. Its totient is φ = 821896990.

The previous prime is 821896979. The next prime is 821896993. The reversal of 821896991 is 199698128.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-821896991 is a prime.

Together with 821896993, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (821896993) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 410948495 + 410948496.

It is an arithmetic number, because the mean of its divisors is an integer number (410948496).

Almost surely, 2^821896991 is an apocalyptic number.

821896991 is a deficient number, since it is larger than the sum of its proper divisors (1).

821896991 is an equidigital number, since it uses as much as digits as its factorization.

821896991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 559872, while the sum is 53.

The square root of 821896991 is about 28668.7458916500. The cubic root of 821896991 is about 936.7113807985.

The spelling of 821896991 in words is "eight hundred twenty-one million, eight hundred ninety-six thousand, nine hundred ninety-one".