81242809 has 4 divisors (see below), whose sum is σ = 81313360. Its totient is φ = 81172260.

The previous prime is 81242773. The next prime is 81242827. The reversal of 81242809 is 90824218.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 81242809 - 2¹³ = 81234617 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81242839) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 33519 + ... + 35860.

It is an arithmetic number, because the mean of its divisors is an integer number (20328340).

Almost surely, 2^81242809 is an apocalyptic number.

It is an amenable number.

81242809 is a deficient number, since it is larger than the sum of its proper divisors (70551).

81242809 is a wasteful number, since it uses less digits than its factorization.

81242809 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 70550.

The product of its (nonzero) digits is 9216, while the sum is 34.

The square root of 81242809 is about 9013.4792949227. The cubic root of 81242809 is about 433.1067746003.

The spelling of 81242809 in words is "eighty-one million, two hundred forty-two thousand, eight hundred nine".