81918820 has 24 divisors (see below), whose sum is σ = 176227128. Its totient is φ = 31968000.

The previous prime is 81918817. The next prime is 81918821. The reversal of 81918820 is 2881918.

It can be written as a sum of positive squares in 4 ways, for example, as 9634816 + 72284004 = 3104^2 + 8502^2 .

It is a self number, because there is not a number n which added to its sum of digits gives 81918820.

It is not an unprimeable number, because it can be changed into a prime (81918821) 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, 49131 + ... + 50770.

It is an arithmetic number, because the mean of its divisors is an integer number (7342797).

Almost surely, 2^81918820 is an apocalyptic number.

It is an amenable number.

81918820 is an abundant number, since it is smaller than the sum of its proper divisors (94308308).

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

81918820 is a wasteful number, since it uses less digits than its factorization.

81918820 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 99951 (or 99949 counting only the distinct ones).

The product of its (nonzero) digits is 9216, while the sum is 37.

The square root of 81918820 is about 9050.9016125467. The cubic root of 81918820 is about 434.3047333504.

The spelling of 81918820 in words is "eighty-one million, nine hundred eighteen thousand, eight hundred twenty".