81290565 has 24 divisors (see below), whose sum is σ = 142204920. Its totient is φ = 42954624.

The previous prime is 81290551. The next prime is 81290581. The reversal of 81290565 is 56509218.

It is a happy number.

81290565 is a `hidden beast` number, since 8 + 1 + 2 + 90 + 565 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 19793601 + 61496964 = 4449^2 + 7842^2 .

It is not a de Polignac number, because 81290565 - 2⁷ = 81290437 is a prime.

It is a super-3 number, since 3×81290565³ (a number of 25 digits) contains 333 as substring.

It is an alternating number because its digits alternate between even and odd.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 3382 + ... + 13191.

It is an arithmetic number, because the mean of its divisors is an integer number (5925205).

Almost surely, 2^81290565 is an apocalyptic number.

It is an amenable number.

81290565 is a deficient number, since it is larger than the sum of its proper divisors (60914355).

81290565 is a wasteful number, since it uses less digits than its factorization.

81290565 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16693 (or 16690 counting only the distinct ones).

The product of its (nonzero) digits is 21600, while the sum is 36.

The square root of 81290565 is about 9016.1280492238. The cubic root of 81290565 is about 433.1916206563.

The spelling of 81290565 in words is "eighty-one million, two hundred ninety thousand, five hundred sixty-five".