81781855 has 4 divisors (see below), whose sum is σ = 98138232. Its totient is φ = 65425480.

The previous prime is 81781853. The next prime is 81781873. The reversal of 81781855 is 55818718.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is not a de Polignac number, because 81781855 - 2¹ = 81781853 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81781853) 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, 8178181 + ... + 8178190.

It is an arithmetic number, because the mean of its divisors is an integer number (24534558).

Almost surely, 2^81781855 is an apocalyptic number.

81781855 is a deficient number, since it is larger than the sum of its proper divisors (16356377).

81781855 is a wasteful number, since it uses less digits than its factorization.

81781855 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16356376.

The product of its digits is 89600, while the sum is 43.

The square root of 81781855 is about 9043.3320739648. The cubic root of 81781855 is about 434.0625515963.

The spelling of 81781855 in words is "eighty-one million, seven hundred eighty-one thousand, eight hundred fifty-five".