81506281 has 2 divisors, whose sum is σ = 81506282. Its totient is φ = 81506280.

The previous prime is 81506267. The next prime is 81506297. The reversal of 81506281 is 18260518.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 71995225 + 9511056 = 8485^2 + 3084^2 .

It is a cyclic number.

It is not a de Polignac number, because 81506281 - 2¹¹ = 81504233 is a prime.

It is a super-2 number, since 2×81506281² = 13286547684901922, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (81506261) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40753140 + 40753141.

It is an arithmetic number, because the mean of its divisors is an integer number (40753141).

Almost surely, 2^81506281 is an apocalyptic number.

It is an amenable number.

81506281 is a deficient number, since it is larger than the sum of its proper divisors (1).

81506281 is an equidigital number, since it uses as much as digits as its factorization.

81506281 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3840, while the sum is 31.

The square root of 81506281 is about 9028.0829083477. The cubic root of 81506281 is about 433.5744606065.

Adding to 81506281 its reverse (18260518), we get a palindrome (99766799).

The spelling of 81506281 in words is "eighty-one million, five hundred six thousand, two hundred eighty-one".