81040581 has 40 divisors (see below), whose sum is σ = 129242520. Its totient is φ = 50429952.

The previous prime is 81040579. The next prime is 81040613. The reversal of 81040581 is 18504018.

81040581 is a `hidden beast` number, since 81 + 0 + 4 + 0 + 581 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 66341025 + 14699556 = 8145^2 + 3834^2 .

It is not a de Polignac number, because 81040581 - 2¹ = 81040579 is a prime.

It is a super-2 number, since 2×81040581² = 13135151537635122, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81040501) by changing a digit.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 315205 + ... + 315461.

It is an arithmetic number, because the mean of its divisors is an integer number (3231063).

Almost surely, 2^81040581 is an apocalyptic number.

81040581 is a gapful number since it is divisible by the number (81) formed by its first and last digit.

It is an amenable number.

81040581 is a deficient number, since it is larger than the sum of its proper divisors (48201939).

81040581 is a wasteful number, since it uses less digits than its factorization.

81040581 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 515 (or 506 counting only the distinct ones).

The product of its (nonzero) digits is 1280, while the sum is 27.

The square root of 81040581 is about 9002.2542176946. The cubic root of 81040581 is about 432.7471157322.

Adding to 81040581 its reverse (18504018), we get a palindrome (99544599).

The spelling of 81040581 in words is "eighty-one million, forty thousand, five hundred eighty-one".