81043561 has 2 divisors, whose sum is σ = 81043562. Its totient is φ = 81043560.

The previous prime is 81043549. The next prime is 81043577. The reversal of 81043561 is 16534018.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 62173225 + 18870336 = 7885^2 + 4344^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81043561 is a prime.

It is not a weakly prime, because it can be changed into another prime (81041561) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40521780 + 40521781.

It is an arithmetic number, because the mean of its divisors is an integer number (40521781).

Almost surely, 2^81043561 is an apocalyptic number.

It is an amenable number.

81043561 is a deficient number, since it is larger than the sum of its proper divisors (1).

81043561 is an equidigital number, since it uses as much as digits as its factorization.

81043561 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2880, while the sum is 28.

The square root of 81043561 is about 9002.4197302725. The cubic root of 81043561 is about 432.7524199497.

Adding to 81043561 its reverse (16534018), we get a palindrome (97577579).

The spelling of 81043561 in words is "eighty-one million, forty-three thousand, five hundred sixty-one".