81075728644 has 9 divisors (see below), whose sum is σ = 141883521717. Its totient is φ = 40537579584.

The previous prime is 81075728639. The next prime is 81075728683. The reversal of 81075728644 is 44682757018.

The square root of 81075728644 is 284738.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in only one way, i.e., 54597930244 + 26477798400 = 233662^2 + 162720^2 .

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 81075728591 and 81075728600.

It is an unprimeable number.

It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 498292 + ... + 640660.

Almost surely, 2^81075728644 is an apocalyptic number.

81075728644 is the 284738-th square number.

It is an amenable number.

81075728644 is a deficient number, since it is larger than the sum of its proper divisors (60807793073).

81075728644 is an frugal number, since it uses more digits than its factorization.

81075728644 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 284742 (or 142371 counting only the distinct ones).

The product of its (nonzero) digits is 3010560, while the sum is 52.

The spelling of 81075728644 in words is "eighty-one billion, seventy-five million, seven hundred twenty-eight thousand, six hundred forty-four".