81928219021 has 4 divisors (see below), whose sum is σ = 89376238944. Its totient is φ = 74480199100.

The previous prime is 81928219019. The next prime is 81928219073. The reversal of 81928219021 is 12091282918.

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 81928219021 - 2¹ = 81928219019 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 (81928219421) 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, 3724009945 + ... + 3724009966.

It is an arithmetic number, because the mean of its divisors is an integer number (22344059736).

Almost surely, 2^81928219021 is an apocalyptic number.

It is an amenable number.

81928219021 is a deficient number, since it is larger than the sum of its proper divisors (7448019923).

81928219021 is a wasteful number, since it uses less digits than its factorization.

81928219021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7448019922.

The product of its (nonzero) digits is 41472, while the sum is 43.

The spelling of 81928219021 in words is "eighty-one billion, nine hundred twenty-eight million, two hundred nineteen thousand, twenty-one".