81539581 has 2 divisors, whose sum is σ = 81539582. Its totient is φ = 81539580.

The previous prime is 81539569. The next prime is 81539617. The reversal of 81539581 is 18593518.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 50836900 + 30702681 = 7130^2 + 5541^2 .

It is a cyclic number.

It is not a de Polignac number, because 81539581 - 2¹⁹ = 81015293 is a prime.

It is a super-3 number, since 3×81539581³ (a number of 25 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81539881) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40769790 + 40769791.

It is an arithmetic number, because the mean of its divisors is an integer number (40769791).

Almost surely, 2^81539581 is an apocalyptic number.

It is an amenable number.

81539581 is a deficient number, since it is larger than the sum of its proper divisors (1).

81539581 is an equidigital number, since it uses as much as digits as its factorization.

81539581 is an evil number, because the sum of its binary digits is even.

The product of its digits is 43200, while the sum is 40.

The square root of 81539581 is about 9029.9269653746. The cubic root of 81539581 is about 433.6334992620.

The spelling of 81539581 in words is "eighty-one million, five hundred thirty-nine thousand, five hundred eighty-one".