81507816205 has 16 divisors (see below), whose sum is σ = 99447228720. Its totient is φ = 64122918912.

The previous prime is 81507816193. The next prime is 81507816227. The reversal of 81507816205 is 50261870518.

It can be written as a sum of positive squares in 8 ways, for example, as 3387007204 + 78120809001 = 58198^2 + 279501^2 .

It is a cyclic number.

It is not a de Polignac number, because 81507816205 - 2¹³ = 81507808013 is a prime.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 459070 + ... + 611359.

It is an arithmetic number, because the mean of its divisors is an integer number (6215451795).

Almost surely, 2^81507816205 is an apocalyptic number.

It is an amenable number.

81507816205 is a deficient number, since it is larger than the sum of its proper divisors (17939412515).

81507816205 is a wasteful number, since it uses less digits than its factorization.

81507816205 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1070688.

The product of its (nonzero) digits is 134400, while the sum is 43.

The spelling of 81507816205 in words is "eighty-one billion, five hundred seven million, eight hundred sixteen thousand, two hundred five".