81720356 has 12 divisors (see below), whose sum is σ = 143838492. Its totient is φ = 40623648.

The previous prime is 81720313. The next prime is 81720409. The reversal of 81720356 is 65302718.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 33640000 + 48080356 = 5800^2 + 6934^2 .

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 58355 + ... + 59738.

It is an arithmetic number, because the mean of its divisors is an integer number (11986541).

Almost surely, 2^81720356 is an apocalyptic number.

It is an amenable number.

81720356 is a deficient number, since it is larger than the sum of its proper divisors (62118136).

81720356 is a wasteful number, since it uses less digits than its factorization.

81720356 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 118270 (or 118268 counting only the distinct ones).

The product of its (nonzero) digits is 10080, while the sum is 32.

The square root of 81720356 is about 9039.9311944284. The cubic root of 81720356 is about 433.9537209885.

The spelling of 81720356 in words is "eighty-one million, seven hundred twenty thousand, three hundred fifty-six".