81855212309 has 8 divisors (see below), whose sum is σ = 88743391800. Its totient is φ = 75051550656.

The previous prime is 81855212287. The next prime is 81855212317. The reversal of 81855212309 is 90321255818.

It can be written as a sum of positive squares in 4 ways, for example, as 3127270084 + 78727942225 = 55922^2 + 280585^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 81855212309 - 2²⁴ = 81838435093 is a prime.

It is a super-2 number, since 2×81855212309² (a number of 23 digits) contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 81855212309.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81855212009) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 21127442 + ... + 21131315.

It is an arithmetic number, because the mean of its divisors is an integer number (11092923975).

Almost surely, 2^81855212309 is an apocalyptic number.

It is an amenable number.

81855212309 is a deficient number, since it is larger than the sum of its proper divisors (6888179491).

81855212309 is a wasteful number, since it uses less digits than its factorization.

81855212309 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 42258919.

The product of its (nonzero) digits is 172800, while the sum is 44.

The spelling of 81855212309 in words is "eighty-one billion, eight hundred fifty-five million, two hundred twelve thousand, three hundred nine".