66191561 has 2 divisors, whose sum is σ = 66191562. Its totient is φ = 66191560.

The previous prime is 66191551. The next prime is 66191563. The reversal of 66191561 is 16519166.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 66113161 + 78400 = 8131^2 + 280^2 .

It is a cyclic number.

It is not a de Polignac number, because 66191561 - 2¹⁴ = 66175177 is a prime.

It is a Sophie Germain prime.

Together with 66191563, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (66191563) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33095780 + 33095781.

It is an arithmetic number, because the mean of its divisors is an integer number (33095781).

Almost surely, 2^66191561 is an apocalyptic number.

It is an amenable number.

66191561 is a deficient number, since it is larger than the sum of its proper divisors (1).

66191561 is an equidigital number, since it uses as much as digits as its factorization.

66191561 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 9720, while the sum is 35.

The square root of 66191561 is about 8135.8196268108. The cubic root of 66191561 is about 404.5146062119.

The spelling of 66191561 in words is "sixty-six million, one hundred ninety-one thousand, five hundred sixty-one".