81505481 has 2 divisors, whose sum is σ = 81505482. Its totient is φ = 81505480.

The previous prime is 81505471. The next prime is 81505483. The reversal of 81505481 is 18450518.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 73188025 + 8317456 = 8555^2 + 2884^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81505481 is a prime.

It is a super-2 number, since 2×81505481² = 13286286866082722, which contains 22 as substring.

It is a Sophie Germain prime.

Together with 81505483, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (81505483) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40752740 + 40752741.

It is an arithmetic number, because the mean of its divisors is an integer number (40752741).

Almost surely, 2^81505481 is an apocalyptic number.

It is an amenable number.

81505481 is a deficient number, since it is larger than the sum of its proper divisors (1).

81505481 is an equidigital number, since it uses as much as digits as its factorization.

81505481 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 6400, while the sum is 32.

The square root of 81505481 is about 9028.0386020442. The cubic root of 81505481 is about 433.5730420626.

Adding to 81505481 its reverse (18450518), we get a palindrome (99955999).

It can be divided in two parts, 8150 and 5481, that added together give a palindrome (13631).

The spelling of 81505481 in words is "eighty-one million, five hundred five thousand, four hundred eighty-one".