81561241 has 4 divisors (see below), whose sum is σ = 81771300. Its totient is φ = 81351184.

The previous prime is 81561229. The next prime is 81561269. The reversal of 81561241 is 14216518.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 14216518 = 2 ⋅7108259.

It can be written as a sum of positive squares in 2 ways, for example, as 6911641 + 74649600 = 2629^2 + 8640^2 .

It is a cyclic number.

It is not a de Polignac number, because 81561241 - 2⁹ = 81560729 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81562241) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 104446 + ... + 105223.

It is an arithmetic number, because the mean of its divisors is an integer number (20442825).

Almost surely, 2^81561241 is an apocalyptic number.

It is an amenable number.

81561241 is a deficient number, since it is larger than the sum of its proper divisors (210059).

81561241 is a wasteful number, since it uses less digits than its factorization.

81561241 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 210058.

The product of its digits is 1920, while the sum is 28.

The square root of 81561241 is about 9031.1262309858. The cubic root of 81561241 is about 433.6718923545.

Adding to 81561241 its reverse (14216518), we get a palindrome (95777759).

The spelling of 81561241 in words is "eighty-one million, five hundred sixty-one thousand, two hundred forty-one".