81281531 has 2 divisors, whose sum is σ = 81281532. Its totient is φ = 81281530.

The previous prime is 81281521. The next prime is 81281533. The reversal of 81281531 is 13518218.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 81281531 - 2¹⁸ = 81019387 is a prime.

It is a super-2 number, since 2×81281531² = 13213374563407922, which contains 22 as substring.

Together with 81281533, it forms a pair of twin primes.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 81281494 and 81281503.

It is not a weakly prime, because it can be changed into another prime (81281533) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40640765 + 40640766.

It is an arithmetic number, because the mean of its divisors is an integer number (40640766).

Almost surely, 2^81281531 is an apocalyptic number.

81281531 is a deficient number, since it is larger than the sum of its proper divisors (1).

81281531 is an equidigital number, since it uses as much as digits as its factorization.

81281531 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1920, while the sum is 29.

The square root of 81281531 is about 9015.6270441939. The cubic root of 81281531 is about 433.1755728813.

Adding to 81281531 its reverse (13518218), we get a palindrome (94799749).

The spelling of 81281531 in words is "eighty-one million, two hundred eighty-one thousand, five hundred thirty-one".