821226991 has 4 divisors (see below), whose sum is σ = 884398312. Its totient is φ = 758055672.

The previous prime is 821226979. The next prime is 821227003. The reversal of 821226991 is 199622128.

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

It is an interprime number because it is at equal distance from previous prime (821226979) and next prime (821227003).

It is a cyclic number.

It is not a de Polignac number, because 821226991 - 2⁹ = 821226479 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 (821226961) 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, 31585641 + ... + 31585666.

It is an arithmetic number, because the mean of its divisors is an integer number (221099578).

Almost surely, 2^821226991 is an apocalyptic number.

821226991 is a deficient number, since it is larger than the sum of its proper divisors (63171321).

821226991 is a wasteful number, since it uses less digits than its factorization.

821226991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 63171320.

The product of its digits is 31104, while the sum is 40.

The square root of 821226991 is about 28657.0583103011. The cubic root of 821226991 is about 936.4567798588.

The spelling of 821226991 in words is "eight hundred twenty-one million, two hundred twenty-six thousand, nine hundred ninety-one".