81921810 has 96 divisors (see below), whose sum is σ = 216732672. Its totient is φ = 19747840.

The previous prime is 81921797. The next prime is 81921857. The reversal of 81921810 is 1812918.

It is a super-2 number, since 2×81921810² = 13422365907352200, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (30).

It is an unprimeable number.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 428815 + ... + 429005.

It is an arithmetic number, because the mean of its divisors is an integer number (2257632).

Almost surely, 2^81921810 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81921810, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (108366336).

81921810 is an abundant number, since it is smaller than the sum of its proper divisors (134810862).

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

81921810 is a wasteful number, since it uses less digits than its factorization.

81921810 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 276 (or 247 counting only the distinct ones).

The product of its (nonzero) digits is 1152, while the sum is 30.

The square root of 81921810 is about 9051.0667879538. The cubic root of 81921810 is about 434.3100172618.

The spelling of 81921810 in words is "eighty-one million, nine hundred twenty-one thousand, eight hundred ten".