81992821 has 4 divisors (see below), whose sum is σ = 82010944. Its totient is φ = 81974700.

The previous prime is 81992803. The next prime is 81992837. The reversal of 81992821 is 12829918.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 12829918 = 2 ⋅6414959.

It is a cyclic number.

It is not a de Polignac number, because 81992821 - 2¹¹ = 81990773 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 (81992221) 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, 4036 + ... + 13426.

It is an arithmetic number, because the mean of its divisors is an integer number (20502736).

Almost surely, 2^81992821 is an apocalyptic number.

It is an amenable number.

81992821 is a deficient number, since it is larger than the sum of its proper divisors (18123).

81992821 is an equidigital number, since it uses as much as digits as its factorization.

81992821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18122.

The product of its digits is 20736, while the sum is 40.

The square root of 81992821 is about 9054.9887354982. The cubic root of 81992821 is about 434.4354697383.

The spelling of 81992821 in words is "eighty-one million, nine hundred ninety-two thousand, eight hundred twenty-one".