81155756805201 has 135 divisors (see below), whose sum is σ = 134984363526243. Its totient is φ = 48568869872640.

The previous prime is 81155756805181. The next prime is 81155756805203. The reversal of 81155756805201 is 10250865755118.

It is a happy number.

The square root of 81155756805201 is 9008649.

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

81155756805201 is a `hidden beast` number, since 8 + 1 + 1 + 5 + 57 + 5 + 68 + 0 + 520 + 1 = 666.

It can be written as a sum of positive squares in 13 ways, for example, as 45257924214801 + 35897832590400 = 6727401^2 + 5991480^2 .

It is not a de Polignac number, because 81155756805201 - 2³¹ = 81153609321553 is a prime.

It is not an unprimeable number, because it can be changed into a prime (81155756805203) by changing a digit.

It is a polite number, since it can be written in 134 ways as a sum of consecutive naturals, for example, 38998440481 + ... + 38998442561.

Almost surely, 2^{81155756805201} is an apocalyptic number.

81155756805201 is a gapful number since it is divisible by the number (81) formed by its first and last digit.

81155756805201 is the 9008649-th square number.

81155756805201 is the 4504325-th centered octagonal number.

It is an amenable number.

81155756805201 is a deficient number, since it is larger than the sum of its proper divisors (53828606721042).

81155756805201 is an frugal number, since it uses more digits than its factorization.

81155756805201 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4274 (or 2134 counting only the distinct ones).

The product of its (nonzero) digits is 3360000, while the sum is 54.

The spelling of 81155756805201 in words is "eighty-one trillion, one hundred fifty-five billion, seven hundred fifty-six million, eight hundred five thousand, two hundred one".