81909072 has 120 divisors (see below), whose sum is σ = 273446784. Its totient is φ = 22378752.

The previous prime is 81909071. The next prime is 81909089. The reversal of 81909072 is 27090918.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81909071) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 21418 + ... + 24950.

Almost surely, 2^81909072 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 81909072, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (136723392).

81909072 is an abundant number, since it is smaller than the sum of its proper divisors (191537712).

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

81909072 is a wasteful number, since it uses less digits than its factorization.

81909072 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3577 (or 3568 counting only the distinct ones).

The product of its (nonzero) digits is 9072, while the sum is 36.

The square root of 81909072 is about 9050.3630866391. The cubic root of 81909072 is about 434.2875058461.

The spelling of 81909072 in words is "eighty-one million, nine hundred nine thousand, seventy-two".