81209085 has 16 divisors (see below), whose sum is σ = 137578176. Its totient is φ = 40763648.

The previous prime is 81209081. The next prime is 81209087. The reversal of 81209085 is 58090218.

It is a happy number.

It is a cyclic number.

It is not a de Polignac number, because 81209085 - 2² = 81209081 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81209081) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 158979 + ... + 159488.

It is an arithmetic number, because the mean of its divisors is an integer number (8598636).

Almost surely, 2^81209085 is an apocalyptic number.

81209085 is a gapful number since it is divisible by the number (85) formed by its first and last digit.

It is an amenable number.

81209085 is a deficient number, since it is larger than the sum of its proper divisors (56369091).

81209085 is a wasteful number, since it uses less digits than its factorization.

81209085 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 318492.

The product of its (nonzero) digits is 5760, while the sum is 33.

The square root of 81209085 is about 9011.6083470155. The cubic root of 81209085 is about 433.0468385702.

It can be divided in two parts, 812090 and 85, that added together give a triangular number (812175 = T₁₂₇₄).

The spelling of 81209085 in words is "eighty-one million, two hundred nine thousand, eighty-five".