66557809 has 2 divisors, whose sum is σ = 66557810. Its totient is φ = 66557808.

The previous prime is 66557807. The next prime is 66557831. The reversal of 66557809 is 90875566.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 46621584 + 19936225 = 6828^2 + 4465^2 .

It is a cyclic number.

It is not a de Polignac number, because 66557809 - 2¹ = 66557807 is a prime.

Together with 66557807, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (66557807) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33278904 + 33278905.

It is an arithmetic number, because the mean of its divisors is an integer number (33278905).

Almost surely, 2^66557809 is an apocalyptic number.

It is an amenable number.

66557809 is a deficient number, since it is larger than the sum of its proper divisors (1).

66557809 is an equidigital number, since it uses as much as digits as its factorization.

66557809 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 453600, while the sum is 46.

The square root of 66557809 is about 8158.2969423771. The cubic root of 66557809 is about 405.2593146999.

The spelling of 66557809 in words is "sixty-six million, five hundred fifty-seven thousand, eight hundred nine".