66667691 has 2 divisors, whose sum is σ = 66667692. Its totient is φ = 66667690.

The previous prime is 66667649. The next prime is 66667697. The reversal of 66667691 is 19676666.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 66667691 - 2¹⁰ = 66666667 is a prime.

It is not a weakly prime, because it can be changed into another prime (66667697) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33333845 + 33333846.

It is an arithmetic number, because the mean of its divisors is an integer number (33333846).

Almost surely, 2^66667691 is an apocalyptic number.

66667691 is a deficient number, since it is larger than the sum of its proper divisors (1).

66667691 is an equidigital number, since it uses as much as digits as its factorization.

66667691 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 489888, while the sum is 47.

The square root of 66667691 is about 8165.0285363861. The cubic root of 66667691 is about 405.4822097617.

Subtracting from 66667691 its reverse (19676666), we obtain a square (46991025 = 6855²).

The spelling of 66667691 in words is "sixty-six million, six hundred sixty-seven thousand, six hundred ninety-one".