81155772 has 18 divisors (see below), whose sum is σ = 205143848. Its totient is φ = 27051912.

The previous prime is 81155741. The next prime is 81155777. The reversal of 81155772 is 27755118.

81155772 is a `hidden beast` number, since 81 + 1 + 5 + 577 + 2 = 666.

It is a tau number, because it is divible by the number of its divisors (18).

It is a Harshad number since it is a multiple of its sum of digits (36), and also a Moran number because the ratio is a prime number: 2254327 = 81155772 / (8 + 1 + 1 + 5 + 5 + 7 + 7 + 2).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81155777) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1127128 + ... + 1127199.

Almost surely, 2^81155772 is an apocalyptic number.

It is an amenable number.

81155772 is an abundant number, since it is smaller than the sum of its proper divisors (123988076).

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

81155772 is a wasteful number, since it uses less digits than its factorization.

81155772 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2254337 (or 2254332 counting only the distinct ones).

The product of its digits is 19600, while the sum is 36.

The square root of 81155772 is about 9008.6498433450. The cubic root of 81155772 is about 432.9520541009.

The spelling of 81155772 in words is "eighty-one million, one hundred fifty-five thousand, seven hundred seventy-two".