81919866 has 24 divisors (see below), whose sum is σ = 190589760. Its totient is φ = 23405592.

The previous prime is 81919861. The next prime is 81919891. The reversal of 81919866 is 66891918.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81919861) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 139026 + ... + 139613.

It is an arithmetic number, because the mean of its divisors is an integer number (7941240).

Almost surely, 2^81919866 is an apocalyptic number.

81919866 is an abundant number, since it is smaller than the sum of its proper divisors (108669894).

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

81919866 is a wasteful number, since it uses less digits than its factorization.

81919866 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 278658 (or 278651 counting only the distinct ones).

The product of its digits is 186624, while the sum is 48.

The square root of 81919866 is about 9050.9593966607. The cubic root of 81919866 is about 434.3065818504.

The spelling of 81919866 in words is "eighty-one million, nine hundred nineteen thousand, eight hundred sixty-six".