81720420 has 96 divisors (see below), whose sum is σ = 237638016. Its totient is φ = 20966400.

The previous prime is 81720409. The next prime is 81720427. The reversal of 81720420 is 2402718.

It is not an unprimeable number, because it can be changed into a prime (81720427) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 290680 + ... + 290960.

It is an arithmetic number, because the mean of its divisors is an integer number (2475396).

Almost surely, 2^81720420 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 81720420, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (118819008).

81720420 is an abundant number, since it is smaller than the sum of its proper divisors (155917596).

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

81720420 is a wasteful number, since it uses less digits than its factorization.

81720420 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 461 (or 459 counting only the distinct ones).

The product of its (nonzero) digits is 896, while the sum is 24.

The square root of 81720420 is about 9039.9347342777. The cubic root of 81720420 is about 433.9538342734.

The spelling of 81720420 in words is "eighty-one million, seven hundred twenty thousand, four hundred twenty".