81899565 has 32 divisors (see below), whose sum is σ = 144986112. Its totient is φ = 39144000.

The previous prime is 81899561. The next prime is 81899569. The reversal of 81899565 is 56599818.

It is an interprime number because it is at equal distance from previous prime (81899561) and next prime (81899569).

It is not a de Polignac number, because 81899565 - 2² = 81899561 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81899561) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 8220 + ... + 15210.

It is an arithmetic number, because the mean of its divisors is an integer number (4530816).

Almost surely, 2^81899565 is an apocalyptic number.

It is an amenable number.

81899565 is a deficient number, since it is larger than the sum of its proper divisors (63086547).

81899565 is a wasteful number, since it uses less digits than its factorization.

81899565 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7081.

The product of its digits is 777600, while the sum is 51.

The square root of 81899565 is about 9049.8378438511. The cubic root of 81899565 is about 434.2707029411.

The spelling of 81899565 in words is "eighty-one million, eight hundred ninety-nine thousand, five hundred sixty-five".