66811891 has 2 divisors, whose sum is σ = 66811892. Its totient is φ = 66811890.

The previous prime is 66811889. The next prime is 66811903. The reversal of 66811891 is 19811866.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 66811891 - 2¹ = 66811889 is a prime.

Together with 66811889, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (66811831) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33405945 + 33405946.

It is an arithmetic number, because the mean of its divisors is an integer number (33405946).

Almost surely, 2^66811891 is an apocalyptic number.

66811891 is a deficient number, since it is larger than the sum of its proper divisors (1).

66811891 is an equidigital number, since it uses as much as digits as its factorization.

66811891 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 20736, while the sum is 40.

The square root of 66811891 is about 8173.8541092926. The cubic root of 66811891 is about 405.7743474161.

The spelling of 66811891 in words is "sixty-six million, eight hundred eleven thousand, eight hundred ninety-one".