81021870 has 80 divisors (see below), whose sum is σ = 227383200. Its totient is φ = 20661696.

The previous prime is 81021859. The next prime is 81021917. The reversal of 81021870 is 7812018.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a Curzon number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 16456 + ... + 20804.

It is an arithmetic number, because the mean of its divisors is an integer number (2842290).

Almost surely, 2^81021870 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81021870, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (113691600).

81021870 is an abundant number, since it is smaller than the sum of its proper divisors (146361330).

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

81021870 is a wasteful number, since it uses less digits than its factorization.

81021870 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4391 (or 4382 counting only the distinct ones).

The product of its (nonzero) digits is 896, while the sum is 27.

The square root of 81021870 is about 9001.2149179986. The cubic root of 81021870 is about 432.7138083265.

Adding to 81021870 its reverse (7812018), we get a palindrome (88833888).

The spelling of 81021870 in words is "eighty-one million, twenty-one thousand, eight hundred seventy".