81408581 has 2 divisors, whose sum is σ = 81408582. Its totient is φ = 81408580.

The previous prime is 81408577. The next prime is 81408601. The reversal of 81408581 is 18580418.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 80263681 + 1144900 = 8959^2 + 1070^2 .

It is a cyclic number.

It is not a de Polignac number, because 81408581 - 2² = 81408577 is a prime.

It is a super-2 number, since 2×81408581² = 13254714120867122, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81408541) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40704290 + 40704291.

It is an arithmetic number, because the mean of its divisors is an integer number (40704291).

Almost surely, 2^81408581 is an apocalyptic number.

It is an amenable number.

81408581 is a deficient number, since it is larger than the sum of its proper divisors (1).

81408581 is an equidigital number, since it uses as much as digits as its factorization.

81408581 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 10240, while the sum is 35.

The square root of 81408581 is about 9022.6703918518. The cubic root of 81408581 is about 433.4011522388.

Adding to 81408581 its reverse (18580418), we get a palindrome (99988999).

The spelling of 81408581 in words is "eighty-one million, four hundred eight thousand, five hundred eighty-one".