821981091 has 4 divisors (see below), whose sum is σ = 1095974792. Its totient is φ = 547987392.

The previous prime is 821981071. The next prime is 821981101. The reversal of 821981091 is 190189128.

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

It is not a de Polignac number, because 821981091 - 2¹⁷ = 821850019 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (821981071) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 136996846 + ... + 136996851.

It is an arithmetic number, because the mean of its divisors is an integer number (273993698).

Almost surely, 2^821981091 is an apocalyptic number.

821981091 is a deficient number, since it is larger than the sum of its proper divisors (273993701).

821981091 is a wasteful number, since it uses less digits than its factorization.

821981091 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 273993700.

The product of its (nonzero) digits is 10368, while the sum is 39.

The square root of 821981091 is about 28670.2126082106. The cubic root of 821981091 is about 936.7433291412.

The spelling of 821981091 in words is "eight hundred twenty-one million, nine hundred eighty-one thousand, ninety-one".