81921800 has 24 divisors (see below), whose sum is σ = 190468650. Its totient is φ = 32768640.

The previous prime is 81921797. The next prime is 81921857. The reversal of 81921800 is 812918.

It can be written as a sum of positive squares in 3 ways, for example, as 80174116 + 1747684 = 8954^2 + 1322^2 .

It is a super-2 number, since 2×81921800² = 13422362630480000, which contains 22 as substring.

It is an unprimeable number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 204605 + ... + 205004.

Almost surely, 2^81921800 is an apocalyptic number.

It is an amenable number.

81921800 is an abundant number, since it is smaller than the sum of its proper divisors (108546850).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

81921800 is a wasteful number, since it uses less digits than its factorization.

81921800 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 409625 (or 409616 counting only the distinct ones).

The product of its (nonzero) digits is 1152, while the sum is 29.

The square root of 81921800 is about 9051.0662355327. The cubic root of 81921800 is about 434.3099995900.

It can be divided in two parts, 8192 and 1800, that multiplied together give a square (14745600 = 3840²).

The spelling of 81921800 in words is "eighty-one million, nine hundred twenty-one thousand, eight hundred".