66565991 has 6 divisors (see below), whose sum is σ = 68941392. Its totient is φ = 64269800.

The previous prime is 66565981. The next prime is 66566011. The reversal of 66565991 is 19956566.

It is a de Polignac number, because none of the positive numbers 2^k-66565991 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66565901) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 38735 + ... + 40416.

It is an arithmetic number, because the mean of its divisors is an integer number (11490232).

Almost surely, 2^66565991 is an apocalyptic number.

66565991 is a deficient number, since it is larger than the sum of its proper divisors (2375401).

66565991 is an equidigital number, since it uses as much as digits as its factorization.

66565991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 79209 (or 79180 counting only the distinct ones).

The product of its digits is 437400, while the sum is 47.

The square root of 66565991 is about 8158.7983796635. The cubic root of 66565991 is about 405.2759202939.

The spelling of 66565991 in words is "sixty-six million, five hundred sixty-five thousand, nine hundred ninety-one".