66549991 has 2 divisors, whose sum is σ = 66549992. Its totient is φ = 66549990.

The previous prime is 66549947. The next prime is 66550009. The reversal of 66549991 is 19994566.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 66549991 - 2⁷ = 66549863 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (66549911) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33274995 + 33274996.

It is an arithmetic number, because the mean of its divisors is an integer number (33274996).

Almost surely, 2^66549991 is an apocalyptic number.

66549991 is a deficient number, since it is larger than the sum of its proper divisors (1).

66549991 is an equidigital number, since it uses as much as digits as its factorization.

66549991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 524880, while the sum is 49.

The square root of 66549991 is about 8157.8177841871. The cubic root of 66549991 is about 405.2434465825.

The spelling of 66549991 in words is "sixty-six million, five hundred forty-nine thousand, nine hundred ninety-one".