81866513 has 2 divisors, whose sum is σ = 81866514. Its totient is φ = 81866512.

The previous prime is 81866489. The next prime is 81866531. The reversal of 81866513 is 31566818.

It is a happy number.

Together with next prime (81866531) it forms an Ormiston pair, because they use the same digits, order apart.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 66129424 + 15737089 = 8132^2 + 3967^2 .

It is a cyclic number.

It is not a de Polignac number, because 81866513 - 2²⁰ = 80817937 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (81826513) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40933256 + 40933257.

It is an arithmetic number, because the mean of its divisors is an integer number (40933257).

Almost surely, 2^81866513 is an apocalyptic number.

It is an amenable number.

81866513 is a deficient number, since it is larger than the sum of its proper divisors (1).

81866513 is an equidigital number, since it uses as much as digits as its factorization.

81866513 is an evil number, because the sum of its binary digits is even.

The product of its digits is 34560, while the sum is 38.

The square root of 81866513 is about 9048.0115495063. The cubic root of 81866513 is about 434.2122759047.

The spelling of 81866513 in words is "eighty-one million, eight hundred sixty-six thousand, five hundred thirteen".