81900820 has 24 divisors (see below), whose sum is σ = 172212264. Its totient is φ = 32718336.

The previous prime is 81900809. The next prime is 81900829. The reversal of 81900820 is 2800918.

It can be written as a sum of positive squares in 4 ways, for example, as 7043716 + 74857104 = 2654^2 + 8652^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81900829) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 16912 + ... + 21208.

It is an arithmetic number, because the mean of its divisors is an integer number (7175511).

Almost surely, 2^81900820 is an apocalyptic number.

It is an amenable number.

81900820 is an abundant number, since it is smaller than the sum of its proper divisors (90311444).

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

81900820 is a wasteful number, since it uses less digits than its factorization.

81900820 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5259 (or 5257 counting only the distinct ones).

The product of its (nonzero) digits is 1152, while the sum is 28.

The square root of 81900820 is about 9049.9071818445. The cubic root of 81900820 is about 434.2729211333.

The spelling of 81900820 in words is "eighty-one million, nine hundred thousand, eight hundred twenty".