81781992 has 24 divisors (see below), whose sum is σ = 221493090. Its totient is φ = 27260640.

The previous prime is 81781991. The next prime is 81782027. The reversal of 81781992 is 29918718.

It can be written as a sum of positive squares in only one way, i.e., 60933636 + 20848356 = 7806^2 + 4566^2 .

It is a tau number, because it is divible by the number of its divisors (24).

It is not an unprimeable number, because it can be changed into a prime (81781991) 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, 567859 + ... + 568002.

Almost surely, 2^81781992 is an apocalyptic number.

It is an amenable number.

81781992 is an abundant number, since it is smaller than the sum of its proper divisors (139711098).

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

81781992 is a wasteful number, since it uses less digits than its factorization.

81781992 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1135873 (or 1135866 counting only the distinct ones).

The product of its digits is 72576, while the sum is 45.

The square root of 81781992 is about 9043.3396486033. The cubic root of 81781992 is about 434.0627939750.

The spelling of 81781992 in words is "eighty-one million, seven hundred eighty-one thousand, nine hundred ninety-two".