81991392 has 48 divisors (see below), whose sum is σ = 245976192. Its totient is φ = 23425920.

The previous prime is 81991387. The next prime is 81991397. The reversal of 81991392 is 29319918.

It is an interprime number because it is at equal distance from previous prime (81991387) and next prime (81991397).

It is a tau number, because it is divible by the number of its divisors (48).

It is a Harshad number since it is a multiple of its sum of digits (42).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81991397) 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, 60334 + ... + 61677.

It is an arithmetic number, because the mean of its divisors is an integer number (5124504).

Almost surely, 2^81991392 is an apocalyptic number.

It is an amenable number.

81991392 is an abundant number, since it is smaller than the sum of its proper divisors (163984800).

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

81991392 is a wasteful number, since it uses less digits than its factorization.

81991392 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 122031 (or 122023 counting only the distinct ones).

The product of its digits is 34992, while the sum is 42.

The square root of 81991392 is about 9054.9098283749. The cubic root of 81991392 is about 434.4329458918.

It can be divided in two parts, 8199 and 1392, that added together give a triangular number (9591 = T₁₃₈).

The spelling of 81991392 in words is "eighty-one million, nine hundred ninety-one thousand, three hundred ninety-two".