81911778 has 16 divisors (see below), whose sum is σ = 176425536. Its totient is φ = 25203600.

The previous prime is 81911771. The next prime is 81911813. The reversal of 81911778 is 87711918.

It is a happy number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (81911771) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 524998 + ... + 525153.

It is an arithmetic number, because the mean of its divisors is an integer number (11026596).

Almost surely, 2^81911778 is an apocalyptic number.

81911778 is an abundant number, since it is smaller than the sum of its proper divisors (94513758).

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

81911778 is a wasteful number, since it uses less digits than its factorization.

81911778 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1050169.

The product of its digits is 28224, while the sum is 42.

The square root of 81911778 is about 9050.5125821690. The cubic root of 81911778 is about 434.2922882591.

The spelling of 81911778 in words is "eighty-one million, nine hundred eleven thousand, seven hundred seventy-eight".