821581821 has 12 divisors (see below), whose sum is σ = 1215674460. Its totient is φ = 534361920.

The previous prime is 821581807. The next prime is 821581823. The reversal of 821581821 is 128185128.

It can be written as a sum of positive squares in 2 ways, for example, as 388484100 + 433097721 = 19710^2 + 20811^2 .

It is not a de Polignac number, because 821581821 - 2²² = 817387517 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (821581823) 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 11 ways as a sum of consecutive naturals, for example, 1112886 + ... + 1113623.

It is an arithmetic number, because the mean of its divisors is an integer number (101306205).

Almost surely, 2^821581821 is an apocalyptic number.

It is an amenable number.

821581821 is a deficient number, since it is larger than the sum of its proper divisors (394092639).

821581821 is a wasteful number, since it uses less digits than its factorization.

821581821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2226556 (or 2226553 counting only the distinct ones).

The product of its digits is 10240, while the sum is 36.

The square root of 821581821 is about 28663.2486121165. The cubic root of 821581821 is about 936.5916329983.

The spelling of 821581821 in words is "eight hundred twenty-one million, five hundred eighty-one thousand, eight hundred twenty-one".