81989821 has 2 divisors, whose sum is σ = 81989822. Its totient is φ = 81989820.

The previous prime is 81989801. The next prime is 81989837. The reversal of 81989821 is 12898918.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 46049796 + 35940025 = 6786^2 + 5995^2 .

It is a cyclic number.

It is not a de Polignac number, because 81989821 - 2²¹ = 79892669 is a prime.

It is a super-2 number, since 2×81989821² = 13444661495224082, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81989801) 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 as a sum of consecutive naturals, namely, 40994910 + 40994911.

It is an arithmetic number, because the mean of its divisors is an integer number (40994911).

Almost surely, 2^81989821 is an apocalyptic number.

It is an amenable number.

81989821 is a deficient number, since it is larger than the sum of its proper divisors (1).

81989821 is an equidigital number, since it uses as much as digits as its factorization.

81989821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 82944, while the sum is 46.

The square root of 81989821 is about 9054.8230794422. The cubic root of 81989821 is about 434.4301712163.

The spelling of 81989821 in words is "eighty-one million, nine hundred eighty-nine thousand, eight hundred twenty-one".