81709236 has 84 divisors (see below), whose sum is σ = 245076832. Its totient is φ = 23339664.

The previous prime is 81709231. The next prime is 81709249. The reversal of 81709236 is 63290718.

It is a tau number, because it is divible by the number of its divisors (84).

It is a Smith number, since the sum of its digits (36) coincides with the sum of the digits of its prime factors.

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

It is a self number, because there is not a number n which added to its sum of digits gives 81709236.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81709231) by changing a digit.

It is a polite number, since it can be written in 27 ways as a sum of consecutive naturals, for example, 18411 + ... + 22413.

Almost surely, 2^81709236 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 81709236, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (122538416).

81709236 is an abundant number, since it is smaller than the sum of its proper divisors (163367596).

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

81709236 is a wasteful number, since it uses less digits than its factorization.

81709236 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4032 (or 4015 counting only the distinct ones).

The product of its (nonzero) digits is 18144, while the sum is 36.

The square root of 81709236 is about 9039.3161245749. The cubic root of 81709236 is about 433.9340368506.

The spelling of 81709236 in words is "eighty-one million, seven hundred nine thousand, two hundred thirty-six".