81705561 has 16 divisors (see below), whose sum is σ = 124656000. Its totient is φ = 46631808.

The previous prime is 81705551. The next prime is 81705563. The reversal of 81705561 is 16550718.

It is not a de Polignac number, because 81705561 - 2⁹ = 81705049 is a prime.

It is a super-3 number, since 3×81705561³ (a number of 25 digits) contains 333 as substring.

It is not an unprimeable number, because it can be changed into a prime (81705563) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 20175 + ... + 23883.

It is an arithmetic number, because the mean of its divisors is an integer number (7791000).

Almost surely, 2^81705561 is an apocalyptic number.

It is an amenable number.

81705561 is a deficient number, since it is larger than the sum of its proper divisors (42950439).

81705561 is a wasteful number, since it uses less digits than its factorization.

81705561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4768.

The product of its (nonzero) digits is 8400, while the sum is 33.

The square root of 81705561 is about 9039.1128436368. The cubic root of 81705561 is about 433.9275311336.

It can be divided in two parts, 8170 and 5561, that added together give a palindrome (13731).

The spelling of 81705561 in words is "eighty-one million, seven hundred five thousand, five hundred sixty-one".