81720224 has 24 divisors (see below), whose sum is σ = 170351748. Its totient is φ = 38456320.

The previous prime is 81720217. The next prime is 81720229. The reversal of 81720224 is 42202718.

It can be written as a sum of positive squares in 2 ways, for example, as 66259600 + 15460624 = 8140^2 + 3932^2 .

It is a super-2 number, since 2×81720224² = 13356390021220352, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 81720193 and 81720202.

It is not an unprimeable number, because it can be changed into a prime (81720229) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 74567 + ... + 75654.

Almost surely, 2^81720224 is an apocalyptic number.

It is an amenable number.

81720224 is an abundant number, since it is smaller than the sum of its proper divisors (88631524).

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

81720224 is a wasteful number, since it uses less digits than its factorization.

81720224 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 150248 (or 150240 counting only the distinct ones).

The product of its (nonzero) digits is 1792, while the sum is 26.

The square root of 81720224 is about 9039.9238934849. The cubic root of 81720224 is about 433.9534873384.

The spelling of 81720224 in words is "eighty-one million, seven hundred twenty thousand, two hundred twenty-four".