81205559 has 2 divisors, whose sum is σ = 81205560. Its totient is φ = 81205558.

The previous prime is 81205547. The next prime is 81205561. The reversal of 81205559 is 95550218.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 81205559 - 2²⁰ = 80156983 is a prime.

Together with 81205561, 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 (81205589) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40602779 + 40602780.

It is an arithmetic number, because the mean of its divisors is an integer number (40602780).

Almost surely, 2^81205559 is an apocalyptic number.

81205559 is a deficient number, since it is larger than the sum of its proper divisors (1).

81205559 is an equidigital number, since it uses as much as digits as its factorization.

81205559 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 18000, while the sum is 35.

The square root of 81205559 is about 9011.4127083382. The cubic root of 81205559 is about 433.0405710233.

The spelling of 81205559 in words is "eighty-one million, two hundred five thousand, five hundred fifty-nine".