81991380 has 24 divisors (see below), whose sum is σ = 229576032. Its totient is φ = 21864352.

The previous prime is 81991369. The next prime is 81991387. The reversal of 81991380 is 8319918.

It is a happy number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81991387) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 683202 + ... + 683321.

It is an arithmetic number, because the mean of its divisors is an integer number (9565668).

Almost surely, 2^81991380 is an apocalyptic number.

It is an amenable number.

81991380 is an abundant number, since it is smaller than the sum of its proper divisors (147584652).

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

81991380 is a wasteful number, since it uses less digits than its factorization.

81991380 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1366535 (or 1366533 counting only the distinct ones).

The product of its (nonzero) digits is 15552, while the sum is 39.

The square root of 81991380 is about 9054.9091657509. The cubic root of 81991380 is about 434.4329246977.

The spelling of 81991380 in words is "eighty-one million, nine hundred ninety-one thousand, three hundred eighty".