81555557 has 2 divisors, whose sum is σ = 81555558. Its totient is φ = 81555556.

The previous prime is 81555547. The next prime is 81555559. The reversal of 81555557 is 75555518.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 50708641 + 30846916 = 7121^2 + 5554^2 .

It is a cyclic number.

It is not a de Polignac number, because 81555557 - 2¹⁴ = 81539173 is a prime.

Together with 81555559, 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 (81555559) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40777778 + 40777779.

It is an arithmetic number, because the mean of its divisors is an integer number (40777779).

Almost surely, 2^81555557 is an apocalyptic number.

It is an amenable number.

81555557 is a deficient number, since it is larger than the sum of its proper divisors (1).

81555557 is an equidigital number, since it uses as much as digits as its factorization.

81555557 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 175000, while the sum is 41.

The square root of 81555557 is about 9030.8115360692. The cubic root of 81555557 is about 433.6618179276.

The spelling of 81555557 in words is "eighty-one million, five hundred fifty-five thousand, five hundred fifty-seven".