81944021 has 4 divisors (see below), whose sum is σ = 82356000. Its totient is φ = 81532044.

The previous prime is 81943993. The next prime is 81944039. The reversal of 81944021 is 12044918.

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.

It is a cyclic number.

It is not a de Polignac number, because 81944021 - 2⁶ = 81943957 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 (81944041) 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, 205691 + ... + 206088.

It is an arithmetic number, because the mean of its divisors is an integer number (20589000).

Almost surely, 2^81944021 is an apocalyptic number.

It is an amenable number.

81944021 is a deficient number, since it is larger than the sum of its proper divisors (411979).

81944021 is a wasteful number, since it uses less digits than its factorization.

81944021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 411978.

The product of its (nonzero) digits is 2304, while the sum is 29.

The square root of 81944021 is about 9052.2936872375. The cubic root of 81944021 is about 434.3492643932.

Adding to 81944021 its reverse (12044918), we get a palindrome (93988939).

The spelling of 81944021 in words is "eighty-one million, nine hundred forty-four thousand, twenty-one".