81661057 has 2 divisors, whose sum is σ = 81661058. Its totient is φ = 81661056.

The previous prime is 81661051. The next prime is 81661061. The reversal of 81661057 is 75016618.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 55487601 + 26173456 = 7449^2 + 5116^2 .

It is a cyclic number.

It is not a de Polignac number, because 81661057 - 2³ = 81661049 is a prime.

It is not a weakly prime, because it can be changed into another prime (81661051) 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, 40830528 + 40830529.

It is an arithmetic number, because the mean of its divisors is an integer number (40830529).

Almost surely, 2^81661057 is an apocalyptic number.

It is an amenable number.

81661057 is a deficient number, since it is larger than the sum of its proper divisors (1).

81661057 is an equidigital number, since it uses as much as digits as its factorization.

81661057 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 10080, while the sum is 34.

The square root of 81661057 is about 9036.6507623123. The cubic root of 81661057 is about 433.8487318536.

The spelling of 81661057 in words is "eighty-one million, six hundred sixty-one thousand, fifty-seven".