81855013 has 2 divisors, whose sum is σ = 81855014. Its totient is φ = 81855012.

The previous prime is 81854987. The next prime is 81855031. The reversal of 81855013 is 31055818.

Together with next prime (81855031) 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., 70845889 + 11009124 = 8417^2 + 3318^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81855013 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81855043) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40927506 + 40927507.

It is an arithmetic number, because the mean of its divisors is an integer number (40927507).

Almost surely, 2^81855013 is an apocalyptic number.

It is an amenable number.

81855013 is a deficient number, since it is larger than the sum of its proper divisors (1).

81855013 is an equidigital number, since it uses as much as digits as its factorization.

81855013 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 4800, while the sum is 31.

The square root of 81855013 is about 9047.3760284405. The cubic root of 81855013 is about 434.1919433136.

The spelling of 81855013 in words is "eighty-one million, eight hundred fifty-five thousand, thirteen".