81309906 has 80 divisors (see below), whose sum is σ = 190270080. Its totient is φ = 25932960.

The previous prime is 81309901. The next prime is 81309919. The reversal of 81309906 is 60990318.

It is a super-2 number, since 2×81309906² = 13222601627457672, which contains 22 as substring.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (81309901) by changing a digit.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 449136 + ... + 449316.

It is an arithmetic number, because the mean of its divisors is an integer number (2378376).

Almost surely, 2^81309906 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81309906, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (95135040).

81309906 is an abundant number, since it is smaller than the sum of its proper divisors (108960174).

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

81309906 is a wasteful number, since it uses less digits than its factorization.

81309906 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 301 (or 292 counting only the distinct ones).

The product of its (nonzero) digits is 11664, while the sum is 36.

The square root of 81309906 is about 9017.2005633678. The cubic root of 81309906 is about 433.2259735349.

It can be divided in two parts, 81309 and 906, that added together give a triangular number (82215 = T₄₀₅).

The spelling of 81309906 in words is "eighty-one million, three hundred nine thousand, nine hundred six".