81639792 has 80 divisors (see below), whose sum is σ = 252379680. Its totient is φ = 25118208.

The previous prime is 81639749. The next prime is 81639809. The reversal of 81639792 is 29793618.

81639792 is a `hidden beast` number, since 8 + 1 + 639 + 7 + 9 + 2 = 666.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1653 + ... + 12884.

It is an arithmetic number, because the mean of its divisors is an integer number (3154746).

Almost surely, 2^81639792 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81639792, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (126189840).

81639792 is an abundant number, since it is smaller than the sum of its proper divisors (170739888).

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

81639792 is a wasteful number, since it uses less digits than its factorization.

81639792 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 14567 (or 14555 counting only the distinct ones).

The product of its digits is 163296, while the sum is 45.

The square root of 81639792 is about 9035.4740882811. The cubic root of 81639792 is about 433.8110696983.

It can be divided in two parts, 8163 and 9792, that added together give a triangular number (17955 = T₁₈₉).

The spelling of 81639792 in words is "eighty-one million, six hundred thirty-nine thousand, seven hundred ninety-two".