81820100 has 36 divisors (see below), whose sum is σ = 179329668. Its totient is φ = 32400000.

The previous prime is 81820073. The next prime is 81820117. The reversal of 81820100 is 102818.

It can be written as a sum of positive squares in 6 ways, for example, as 21104836 + 60715264 = 4594^2 + 7792^2 .

It is a Harshad number since it is a multiple of its sum of digits (20).

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 6050 + ... + 14150.

Almost surely, 2^81820100 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81820100, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (89664834).

81820100 is an abundant number, since it is smaller than the sum of its proper divisors (97509568).

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

81820100 is a wasteful number, since it uses less digits than its factorization.

81820100 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8216 (or 8209 counting only the distinct ones).

The product of its (nonzero) digits is 128, while the sum is 20.

The square root of 81820100 is about 9045.4463682010. The cubic root of 81820100 is about 434.1302036657.

Adding to 81820100 its reverse (102818), we get a palindrome (81922918).

The spelling of 81820100 in words is "eighty-one million, eight hundred twenty thousand, one hundred".