66697991 has 2 divisors, whose sum is σ = 66697992. Its totient is φ = 66697990.

The previous prime is 66697951. The next prime is 66698003. The reversal of 66697991 is 19979666.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 66697991 - 2¹⁴ = 66681607 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 (66697951) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33348995 + 33348996.

It is an arithmetic number, because the mean of its divisors is an integer number (33348996).

Almost surely, 2^66697991 is an apocalyptic number.

66697991 is a deficient number, since it is larger than the sum of its proper divisors (1).

66697991 is an equidigital number, since it uses as much as digits as its factorization.

66697991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1102248, while the sum is 53.

The square root of 66697991 is about 8166.8837998345. The cubic root of 66697991 is about 405.5436300685.

The spelling of 66697991 in words is "sixty-six million, six hundred ninety-seven thousand, nine hundred ninety-one".