81235209 has 16 divisors (see below), whose sum is σ = 119335104. Its totient is φ = 48744000.

The previous prime is 81235207. The next prime is 81235249. The reversal of 81235209 is 90253218.

It is a happy number.

It is not a de Polignac number, because 81235209 - 2¹ = 81235207 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (81235207) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 8854 + ... + 15519.

It is an arithmetic number, because the mean of its divisors is an integer number (7458444).

Almost surely, 2^81235209 is an apocalyptic number.

It is an amenable number.

81235209 is a deficient number, since it is larger than the sum of its proper divisors (38099895).

81235209 is a wasteful number, since it uses less digits than its factorization.

81235209 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 24488.

The product of its (nonzero) digits is 4320, while the sum is 30.

The square root of 81235209 is about 9013.0576942567. The cubic root of 81235209 is about 433.0932689368.

Subtracting 81235209 from its reverse (90253218), we obtain a square (9018009 = 3003²).

The spelling of 81235209 in words is "eighty-one million, two hundred thirty-five thousand, two hundred nine".