81265781 has 2 divisors, whose sum is σ = 81265782. Its totient is φ = 81265780.

The previous prime is 81265777. The next prime is 81265783. The reversal of 81265781 is 18756218.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 78676900 + 2588881 = 8870^2 + 1609^2 .

It is a cyclic number.

It is not a de Polignac number, because 81265781 - 2² = 81265777 is a prime.

It is a super-2 number, since 2×81265781² = 13208254323079922, which contains 22 as substring.

Together with 81265783, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81265783) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40632890 + 40632891.

It is an arithmetic number, because the mean of its divisors is an integer number (40632891).

Almost surely, 2^81265781 is an apocalyptic number.

It is an amenable number.

81265781 is a deficient number, since it is larger than the sum of its proper divisors (1).

81265781 is an equidigital number, since it uses as much as digits as its factorization.

81265781 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 26880, while the sum is 38.

The square root of 81265781 is about 9014.7535185384. The cubic root of 81265781 is about 433.1475921256.

The spelling of 81265781 in words is "eighty-one million, two hundred sixty-five thousand, seven hundred eighty-one".