81865558516 has 36 divisors (see below), whose sum is σ = 166679381988. Its totient is φ = 35080082688.

The previous prime is 81865558451. The next prime is 81865558517. The reversal of 81865558516 is 61585556818.

It can be written as a sum of positive squares in 2 ways, for example, as 77727209616 + 4138348900 = 278796^2 + 64330^2 .

It is a super-2 number, since 2×81865558516² (a number of 23 digits) contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81865558517) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 1500630 + ... + 1554226.

It is an arithmetic number, because the mean of its divisors is an integer number (4629982833).

Almost surely, 2^81865558516 is an apocalyptic number.

It is an amenable number.

81865558516 is an abundant number, since it is smaller than the sum of its proper divisors (84813823472).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

81865558516 is a wasteful number, since it uses less digits than its factorization.

81865558516 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 61408 (or 61399 counting only the distinct ones).

The product of its digits is 11520000, while the sum is 58.

The spelling of 81865558516 in words is "eighty-one billion, eight hundred sixty-five million, five hundred fifty-eight thousand, five hundred sixteen".