66661813 has 2 divisors, whose sum is σ = 66661814. Its totient is φ = 66661812.

The previous prime is 66661789. The next prime is 66661817. The reversal of 66661813 is 31816666.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 39225169 + 27436644 = 6263^2 + 5238^2 .

It is a cyclic number.

It is not a de Polignac number, because 66661813 - 2⁵ = 66661781 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (66661817) 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, 33330906 + 33330907.

It is an arithmetic number, because the mean of its divisors is an integer number (33330907).

Almost surely, 2^66661813 is an apocalyptic number.

It is an amenable number.

66661813 is a deficient number, since it is larger than the sum of its proper divisors (1).

66661813 is an equidigital number, since it uses as much as digits as its factorization.

66661813 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 31104, while the sum is 37.

The square root of 66661813 is about 8164.6685786993. The cubic root of 66661813 is about 405.4702924724.

The spelling of 66661813 in words is "sixty-six million, six hundred sixty-one thousand, eight hundred thirteen".