81871821 has 24 divisors (see below), whose sum is σ = 120967704. Its totient is φ = 53343360.

The previous prime is 81871819. The next prime is 81871831. The reversal of 81871821 is 12817818.

It can be written as a sum of positive squares in 4 ways, for example, as 16892100 + 64979721 = 4110^2 + 8061^2 .

It is not a de Polignac number, because 81871821 - 2¹ = 81871819 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81871831) 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 in 23 ways as a sum of consecutive naturals, for example, 107775 + ... + 108531.

It is an arithmetic number, because the mean of its divisors is an integer number (5040321).

Almost surely, 2^81871821 is an apocalyptic number.

It is an amenable number.

81871821 is a deficient number, since it is larger than the sum of its proper divisors (39095883).

81871821 is a wasteful number, since it uses less digits than its factorization.

81871821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1021 (or 1018 counting only the distinct ones).

The product of its digits is 7168, while the sum is 36.

The square root of 81871821 is about 9048.3048688691. The cubic root of 81871821 is about 434.2216600793.

The spelling of 81871821 in words is "eighty-one million, eight hundred seventy-one thousand, eight hundred twenty-one".